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CERC WAVE GAGES

Leo C. Williams

DATA LIBRARY & ARCHIVES

Woods Hole Oceanographic > inatitution

TECHNICAL MEMORANDUM NO. 30

DECEMBER 1969

U. S. ARMY, CORPS OF ENGINEERS ©

COASTAL ENGINEERING
- RESEARCH CENTER —

_ This document has been approved for public release and sale;
its distribution is unlimited.

Reprint or republication of any of this material
shall give appropriate credit to the U. S. Army Coastal
Engineering Research Center.

Limited free distribution within the United States
of single copies of this publication is made by:

Coastal Engineering Research Center
5201 Little Falls Road, N.W.
Washington, D. C. 20016

Contents of this report are not to be used for
advertising, publication, or promotional purposes.
Citation of trade names does not constitute an official
endorsement or approval of the use of such commercial
products.

The findings in this report are not to be construed
as an official Department of the Army position unless
so designated by other authorized documents.

CERC WAVE GAGES

Leo C. Williams

TECHNICAL MEMORANDUM NO. 30
DECEMBER 1969

0 0301 0045172 O

U. S. ARMY, CORPS OF ENGINEERS

COASTAL ENGINEERING
RESEARCH CENTER

HN AAU

This document has been approved for public release and sale;
its distribution is unlimited.

ABSTRACT

CERC has used wave gages to gather prototype wave data since 1948.
Two basic types of gages are now used in the field - the step-resistance
staff gage and the underwater pressure-sensitive gage. CERC has developed
three types of step-resistance staff gages - a series type for use in
fresh water, a parallel type for use in salt water, and a relay-operated
type for use in either fresh or salt water or in water where wide changes
in salinity occur. The pressure gage can be used in water of any salinity.
The series and parallel gages have an accuracy of +5 percent plus the
spacing of one sensor increment. The relay gage has an accuracy of +2
percent plus the spacing of one sensor increment. The accuracy of the
pressure-sensitive gage is not as precise as that of the step-resistance
gages.

The report describes each gage and the theory of operation, details
of fabrication, steps for calibration and installation, and requirements
of maintenance.

FOREWORD

This report describes in detail the sensors and recorders used by
CERC in wave-data collection programs. Leo C. Williams, Chief of the
Instrumentation and Equipment Branch, Research Division, prepared this
report and developed most of the wave-data equipment used at CERC.
Thorndike Saville, Jr. is Chief of the Research Division. The
Manuscript was prepared in 1966.

Many drawings in this publication have been greatly reduced from
the originals. The large originals are available at CERC in limited
quantities.

At the time of publication, Lieutenant Colonel Edward M. Willis
was Director of the Center; Joseph M. Caldwell was Technical Director.

NOTE: Comments on this publication are invited. Discussion will be
published in the next issue of the CERC Bulletin.

This report is published under authority of Public Law 166, 79th
Congress, approved July 31, 1945, as supplemented by Public Law 172,
88th Congress, approved November 7, 1963.

Section

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CONTENTS

I. INTRODUCTION .

Wave Program at CERC ..... .

Recording and Analysis

Types of Wave Gages

II. SERIES-TYPE, STEP-RESISTANCE GAGE FOR USE IN FRESH
WATER . STO PRE auals Hoe, MEPS eCKe) aes hob

Theory of Operation of Series-Type, Step-Resistance Gage

Fabrication of Series-Type, Step-Resistance Gage
Operation of a Series-Type, Step-Resistance Wave Gage .

III. PARALLEL-TYPE, STEP-RESISTANCE GAGE FOR SALT WATER .

Theory of Operation of Parallel-Type, Step-Resistance Gage
Fabrication of a Parallel-Type, Step-Resistance Gage
Operation of Parallel-Type, Step-Resistance Gage

IV. RELAY-TYPE,STEP-RESISTANCE GAGE FOR SALT AND FRESH
WASTE Ro camer omerce omc camsiuet ghallshn “oy tralia Sec titers eM ere arate \eetan ea rcimige ate a

Theory of Operation of a Relay-Type, Step-Resistance Gage .

Fabrication of a Relay-Operated Step-Resistance Gage
Operation of a Relay-Type, Step-Resistance Gage .

V. PRESSURE-SENSITIVE GAGE
Theory of Operation of Pressure-Sensitive Gage
Fabrication of a Pressure-Sensitive Gage
Operation of Pressure-Sensitive Gage

VI. FABRICATION OF EPOXY GAGE SECTION .

VII. MAGNETIC TAPE RECORDER FOR OCEAN-WAVE GAGES
Theory of Operation of Magnetic Tape Recorder .
Fabrication of Magnetic Tape Recorder .
Calibration and Operation .

VIII. MODIFICATION OF STRIP-CHART RECORDER SPEED

IX. ANALYSIS OF OCEAN-WAVE GAGE RECORDS

Step-Resistance Wave Gages
Pressure-Sensitive Gages

Tables

IIl

ILLUSTRATIONS

Resistance Values in Ohms for 20-Foot Gage for Fresh Water
Resistance Values in Ohms for 25-Foot Series Gage .

Components for 25-Foot Five-Section Fresh-Water
Series-Resistance Gage

List of Components for Wave-Gage Holder . .

Resistor Values for Salt-Water Parallel Step-Resistance
Wave Gage Rul Ass tere eomrcr me ten to: bd acs: <r, Wo Sem

Components for Five-Section 25-Foot Parallel Resistance
Gage for Salt Water ......

Components for Five-Section 25-Foot Relay Staff Gage
Resistor Values in Ohms for 125-Point Relay Gage

List of Components for Pressure-Sensitive Gage, Model BE-2.
List of Components for Magnetic Tape Recorder, LW-1

Parts Required for a Calibration Unit for Calibration of
a Tape Recorder with a Strip-Chart Recorder .

° e

Figures

Block Diagram of Series-Type Step-Resistance Gage for
[BCS EMEC oN oii do ooo 900 oo eee -9)G se lsd' lo. 6

Block Diagram of Parallel Step-Resistance Gage for Salt Water 5

Block Diagram of Relay-Operated Step-Resistance Gage
Block Diagram of Pressure-Sensitive Wave Gage .

Series-Type, Step-Resistance Gage for Fresh Water .

Series-Type, Step-Resistance Gage for Fresh Water. ... .

Practical Circuit for Measuring Wave Heights in Fresh Water

Series-Type Step-Resistance Wave Gage for Use in Fresh Water

Figures

Qe
10.
ll.
Wee
13.
14.
ILSye

16.

17.
18.
19.

20.

21.

22.

23.
24.
25.
26.
27.

28.

29.
30.

31.

Power unit for Fresh-Water Staff Gage .

Programmer for Wave Gages

Signal Input Cable for Strip-Chart Recorder .
Holder for Sectional Step-Resistance Gage Sections
Pile Clamp for Wave Gage

Diagram of Fresh-Water Staff Gage .

Wiring Diagram for Fresh-Water Gage Section .

Functional Block Diagram of Parallel-Type, Step-Resistance
Gage for Salt Water. Baily haynes

Functional Diagram for Parallel Resistor Gage .
Parallel-type, Step-Resistance Gage for Use in Salt Water .
Transformer Unit for Salt-Water Gage

Wiring Diagram of Transformer Unit of Parallel Step-
Resistance Gage .

Panel Assembly for Parallel-Resistance Gage .

Wiring Diagram for Power SOG and ee of Parallel
Step-Resistance Gage .

Connecting Diagram for Parallel Step-Resistance Gage Section
Hookup Diagram for Parallel-type Step-Resistance Gage .
Simplified Diagram of Relay-type, Step-Resistance Gage
Modified Circuit for Relay-type, Step-Resistance Gage .
Simplified Diagram for Relay Gage .

Relay-Operated Step-Resistance Wave Gage for use in
Fresh or Salt Water

Relay-panel Layout for Relay-type Gage
Front Panel and Chassis Drilling for Relay-type Gage

Relay Panel - A, B, C, D, E.

Page

Figures
32. Power Supply for Relay Staff Gage .......
33. Cabinet Assembly for Relay-type, Step-Resistance Gage .
34. Block Diagram for Relay Staff Gage
35. Parts and Assembly Drawing of Pressure-Sensitive Gage .
36. Washers for Blocking Bellows of Pressure Gage .
37. Power Supply Unit for Amplifier of Pressure-Sensitive Gage
38. Amplifier Power-Supply Unit for Pressure Gage .
39. Concrete Block for Mounting Pressure-Sensitive Gage .
40. Diagram for Pressure-Sensitive Gage
41. Patterns, Container, and Molds for Epoxy Sections for

Step-Resistance Gages AS nee ee :

42. Parts for Magnetic Tape Recorder, LW 1
43. Magnetic Tape Recorder Panel Layout, Model LW-1
44. Chassis Layout for Model LW-1 Magnetic Tape Recorder
45. Chassis Layout for Model LW-1 Magnetic Tape Recorder
46. Schematic Diagram for Magnetic Tape Recorder, Model LW-1
47. Calibration Signal Timer for Magnetic Tape Recorder .
48. Diagram of Calibration Unit
49. Magnetic Tape Recorder, Model LW-1
50. Block Diagram of Calibration Hookup .
51. Wave Records with Chart Speed of 2.5 mm per second
52. Wave Records with Chart Speed of 1.25 mm per second .
53. Wave Records with Chart Speed of 1.0 mm per second
54. Gear Modification of Brush Recorder Chart Drive to

furnish chart speeds of 2.5, 12.5, 62.5 mm per second

Page
53
54
60
65
68
70
71
72

80
88
89
90
sil
92
94

97
99
102
103

104

105

Figures

55.

56.

57.

58.

59.

60.

61.

62.

63.

Gear Modification of Brush Recorder Chart Drive to furnish
chart speeds of 1.25, 6.25, or 31.25 mm per second

Gear Modification of Brush Recorder Chart Drive to
furnish chart speeds of 1.0, 5.0, 25.0 mm per second

Gear Train Brush Recorder prior to modification
Gear Train Brush Recorder after Modification .
Sample Wave-period Template

Sample of Wave-height Template .

Wave-data Compilation Sheet

Pressure Response Curves for Various Depths and Wave
Periods .

vii

Page

106

107
109
110
112
113
114

115

116

‘
igh

Section I. INTRODUCTION
1. Wave Program at CERC

The Coastal Engineering Research Center (CERC), formerly the
Beach Erosion Board, has been collecting data from wave gages for more
than 20 years. The program started in April 1948, when the first gages
were installed in New Jersey. Since then, many gages have been installed.
In addition to gages on the Atlantic, Gulf of Mexico, and Pacific shores,
gages have been installed in the Great Lakes, at Hawaii, and in smaller
inland lakes and reservoirs.

Signals from 7 locations and 10 gages are now instantaneously re-
corded on a central panel in the CERC Laboratory. These signals are
carried by leased telephone lines.

CERC uses two basic types of wave gages - the step-resistance staff
gage and the pressure-sensitive gage. The more accurate is the step-
resistance gage and it is favored for use in locations where a structure
is available for its installation or where the construction of a suitable
support is feasible. The pressure-sensitive underwater gage is selected
for those sites where a less accurate gage is acceptable for a measure-
ment program, and where the measurement of waves with periods of less
than 4 seconds is not required.

2. Recording and Analysis

Recordings from both types of gages are normally produced on a
pen and ink paper strip-chart recorder. The length of time that the
waves are recorded is selected in accordance with the mission of the
individual gage or within the overall program of wave study. Automatic
programming of the gage recording time is normally provided along with
a control for manual selection of special recording periods.

Tide changes are not normally removed from the strip-chart record-
ings taken with the staff type step-resistance wave gage. However, tide
removal can be provided for this gage should the requirement for this
type operation arise. Tide changes are removed from the pressure-
sensitive wave gage. If such removal was not incorporated in the gage
operation, barometric changes would also be present in the recording,
thus a record that would be difficult to analyze would be produced.

Data from both types of wave gages may be recorded on magnetic tape.
Records made on magnetic tape are analyzed on a spectrum analyzer in the
CERC Laboratory. The analyzer performs the following analyses from a
20-minute recording:

a) Linear average wave height.
b) Squared average wave height.
c) Linear peak wave height.

d) Squared peak wave height.
e) Linear integrated wave height.
f) Squared integrated wave height.

These values are presented on the vertical axis of the spectral
plot with the corresponding wave period presented’on the horizontal
axdSOf themplot.

The magnetic tape recorder usually records wave conditions continu-
ously using a tape speed of 1/2 inch per minute. One roll of 1/4 inch
wide magnetic tape 1,250 feet long, records continuously for approximately
3 weeks.

The magnetic tape recorder has a built-in calibration generator (sine
wave) with a period of 4 seconds. The calibration signal is adjusted to
provide an amplitude equal to that produced by the wave gage for full-
scale recording on the strip chart and magnetic tape. This calibration
signal is recorded for 30 minutes every 12 hours to provide a standard-
ization signal to compensate for changes found in magnetic tape from roll
to roll, and to calibrate the entire spectrum analyzer in the laboratory.
The calibration signal is timed by a program clock connected with the
tape recorder.

3. Types of Wave Gages

The staff type step-resistance wave gage is available for three
different applications:

a) Series step-resistance type for use in fresh water.

b) Parallel step-resistance type for use in salt water loca-
tions where little or no change occurs in salinity.

c) Relay-operated step-resistance type that will operate in
either fresh water or salt water and where wide changes
in salinity occur.

The accuracy of the recording taken with the fresh-water, series,
step-resistance gage and the salt-water, parallel, step-resistance gage
is about plus or minus 5 percent, plus the spacing of one staff-sensing
point.

The accuracy of the recording taken with the relay-operated step-
resistance gage is about plus or minus 2 percent plus the spacing of one
staff sensing point. Due to the increased accuracy expected of this gage,
servicing and cleaning of the sensing elements may have to be performed
more often than on the other two step-resistance gages. This service
will depend on local conditions of sea growth at the gage site.

The sensing units for the staff type step-resistance wave gages are
molded from epoxy resin in 5-foot lengths, and are stacked in a steel or

aluminum holder to provide the gage length desired for the location,
usually 15 to 25 feet. Sensing contacts are molded into the 5-foot
sections at intervals to provide the incremental accuracy required
of the gage. Sensing contacts spaced every 0.2 foot have been found
adequate for gages with lengths of 15 to 25 feet. Sensing contacts
spaced 0.1 foot have been used on gages of 10 feet or less.

The sensing unit for the pressure-sensitive underwater wave gage
senses the change in pressure produced by the increase (or decrease) in
water height as the wave passes over the gage. The change in pressure
produced by a wave with an 8-second period with a height of 4 feet on a
gage submerged in 30 feet of water will be less than that produced by
the same wave on the same wave gage submerged in 10 feet of water. A
wave with a period shorter than 8 seconds and with a height of 4 feet
will produce less pressure at both the 30-foot and 10-foot depths than
the 8-second wave. This phenomena is referred to as a pressure gradient
condition produced as a function of wave height versus wave period versus
water depth to the sensing element.

The pressure-sensing element used by the CERC is designed for use
in locations where the total water depth (stillwater depth plus height
of wave crest) is less than 50 feet. Sensing elements with similar
characteristics that are interchangeable with the CERC model except for
the d.c. power requirements are available from commercial sources. One
of these is Fairchild Semi-Conductor Corporation Model TF 150 series.
These sensors are available in a variety of pressure ranges and may be
used in water depths greater than the 50-foot total range of the CERC
model. However, use of a pressure-sensitive gage in water depths greater
than 30 feet is not advised due to the depth-period attenuation factor
of recordings taken from such an installation.

Figure 1 shows a block diagram of the components used in a2 series-
type step-resistance wave gage for use in fresh water.

Figure 2 shows a block diagram of a parallel-type step-resistance
wave gage for use in salt water.

Figure 3 shows a block diagram of a relay-operated step-resistance
wave gage for use in water of varying salinity.

Figure 4 shows a block diagram of a pressure-sensitive wave gage.

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Section II. SERIES-TYPE, STEP-RESISTANCE GAGE FOR USE IN FRESH WATER

1. Theory of Operation of Series-Type, Step-Resistance Gage

The series-type, step-resistance gage operates on the principle
of a simple series-type circuit with a constant voltage d.c. source, a
recorder penmotor and a variable resistor connected in series. Figure 5
shows a simple series circuit containing a constant voltage source, the
penmotor, and a variable resistance.

CONSTANT VOLTAGE RECORDER Recorder Pen
(D.C. Source) PEN MOTOR

Variable Resistor

Figure 5. Series-Type, Step-Resistance Gage for Fresh Water

The recorder penmotor is essentially the same as an ordinary
D'Arsonval panel-meter movement with a capillary, ink pen substituted
for the indicating pointer. The components (magnet, moving coil, springs,
etc.) are significantly larger and more rugged than the ordinary meter
movement.

The variable resistor used in a gage consists of several fixed re-
sistors in series with contact tips connected to the resistor junctions.
The contact tips are molded into long epoxy resin shapes that allow the
contact tips to be exposed. The number of contacts submerged by the
part of the gage that is under water forms the variation in resistance.

The constant voltage d.c. source is obtained from a transformer,
rectifier, filter, and voltage regulator operated from a 115-volt, 60-
cycle power line. The output voltage from these components is constant
even though the input line voltage may vary from about 95 to 130 volts
and thus prevents the recorder penmotor from changing with a varying
line voltage.

Since the voltage source is constant and the resistance of the pen-
motor is constant (neglecting temperature changes), the current in the
circuit will increase if the value of the variable resistor is decreased.
Ohms law, E = IR, applies.

The recorder penmotor is designed to provide a linear pen movement
with a linear change in input current.

The nominal current required to move the penmotor pen through a 50-
millimeter arc (full scale) is 20 milliamperes. The penmotor has a
nominal internal resistance of 1,500 ohms, thus by ohms law the constant
voltage source will be a nominal 30 volts (E = IR; .02 x 1,500 = 30 volts)
for the required pen movement.

To make the penmotor move in equal increments from a variable resis-
tor made of several resistors connected in series as shown in Figure 6,
it is necessary to calculate each individual resistor value.

CONSTANT VOLTAGE RECORDER
(D.C. Source) PEN MOTOR

Movable Contact
Figure 6. Series-Type, Step-Resistance Gage for Fresh Water.

Assuming a wave gage with 20 equal measurement increments and a pen-
motor with an internal resistance of 1,500 ohms that requires 20 milli-
amperes for full-scale movement and that indicates linearly with a change
in current, then to move the pen full scale, 20 current changes of 1
milliampere each would be required. A 30-volt power source would provide
full-scale penmotor movement.

30 volts ig
aSOUNGHTISN .02 amperes

The first of the 20 intervals of gage measurement would reduce the
20-milliampere penmotor current by 1 milliampere.

To calculate the first gage resistor:

30 volts

19 milliamperes — 1°79 ohms.

1,579 ohms total circuit resistance minus 1,500 ohm penmoter resistance =
79 ohms (first resistor).

To calculate the second resistor value:

30 volts ___s= _‘1,667 ohms - 1,579 = 88 ohms.
18 milliamperes

To calculate the third resistor:

30 volts

«(1 =*7.765 ohms - 1,667 ohms = 98 ohms.
17 milliamperes

Such calculation shows that the resistors will not be of equal value
to obtain equal increments of pen movement. The individual resistor values
will be higher at the left and lower on the right side of the resistor
string in Figure 6.

The circuit in Figure 6 applied to a practical circuit for measuring
wave heights in fresh water is shown in Figure 7.

The major difference between the two circuits (Figures 6 and 7) is
that the water path is now used to activate the changes in the variable
resistor. Another change is the addition of a variable calibration re-
sistor to adjust for differences in the conductivity of fresh water and
differences in penmotors. Analysis of this circuit shows that the bottom
resistor in the gage circuit is connected to the ground rod. This con-
nection is necessary due to the electrical resistance of the residual water
path on the epoxy resin when the gage submergence is small. Further analy-
sis of the circuit shows that the water path has a resistance of its own,
therefore, some current will flow from each submerged metal senSing tip to
the ground rod; such flow will aid in reducing the effective resistance
of the water path.

Using the 30-volt source previously calculated as required to provide
full-scale penmotor operation in the practical gage circuit in Figure 6,
it is found that the recorder penmotor will not rise to full scale. This
is due to the added resistance of the water path. To compensate for the
increased resistance, it is necessary to increase the voltage from the
constant d.c. voltage source. The increased resistance path will also
change the direct logic used for Figure 6 in calculating the resistors for
the gage.

Design experience has resulted in the selection of a d.c. voltage
source of 46 and 54 volts as the best value for most fresh-water applica-
tions. This same experience has resulted in the resistor values shown in
Tables I and II for 20- and 25-foot series-type gages. If a 10-foot gage
is desired, it is recommended that the spacing of the sensing tips be used
to 0.1 foot and the resistor values for the 20-foot gage be used.

There will be some electrolytic action in the water path due to the
use of direct current. This action usually causes a hard powder to form
on the lead sensing tips of the gage. Rate of coating formation depends
on the mineral content of the local water. The gage must be cleaned of
the deposit to obtain the most accurate operation. Frequency of cleaning

Text resumes on page 16

RECORDER Recorder

PEN MOTOR

CONSTANT VOLTAGE
(D.C. Source)

Pen

Variable Calibration Resistor

Ground Rod

Individual Resistors Molded
into Epoxy Resin Wave
Staff Units.

Metal Sensing Tips

Figure 7. Practical circuit for measuring wave heights in fresh water.

TABLE I

RESISTANCE VALUES IN OHMS FOR 20-FOOT GAGE FOR FRESH WATER

seers A Section B Section C eons D
24 41 83 267
24 41 87 286
24 42 90 305
25 43 93 326
26 45 96 351
26 45 101 Si,
26 47 104 408
27 48 109 441
28 50 113 ~ 480
28 50 118 522
29 53 123 Siz
29 53 129 629
30 55 134 695
30 57 141 771
31 59 147 861
32 60 155 968
33 62 162 1096
33 64 171 1251
34 67 179 1441
35 68 189 1678
36 70 200 1980
37 73 210 2370
38 75 224 2888
38 78 236 3598
39 eels 252 4606

TW - 427, BOG 23 O61 i

Z
Oo ON DO FP WY YF |O

NN NY NH NHN DD BF FY BF YY BF FY PF BY eB eS
anf WNH KF OO DMN Aun fF WN FS OC

RESISTANCE VALUES IN OHMS FOR 25-FOOT SERIES GAGE

Top

Section A

22
21
23
23
24
23
25
24
25
25
26
26
26
27
27
28
28
29
29
30
30
31
32
32
32

Section B

33
34
34
35
36
36
37
38
38
39
40
41
42
42
44
44
45
47
47
48
50
50
51
53
55

Section C

TABLE

55
56
59
59
61
62
64
66
67
70
ma
73
75
77
79
81
84
87
88
92
95
97
101
103
108

Section D

110
115
118
123
128
131
137
142
147
154
159
166
173
180
188
197
205
215
226
236
249
261
275
291
306

Bottom
Section E

324
343
365
387
412
441
471
504
543
585
632
686
746
814
894
983
1089
1212
NSS7/
1530
1738
1961

TABLE III
COMPONENTS FOR 25-FOOT FIVE-SECTION FRESH-WATER SERIES-RESISTANCE GAGE

1. Strip-Chart Recorder Brush #RD-2321-00. Order with following ears
modifications: single channel operation with 50 mm chart width.
Old style penmotor #BL 902 and long pen #BL 921.

2. Chart rewind Brush #RA-2402-10 1 ea.

3. Constant voltage power supply 48-52 volts 100 MA Technipower
#M-50.0 - 0.100, or equal.

4. Toggle Switch SPST AH&H #20994-BF Zuea
5. Potentiometer 1.5K Mallory #M1.5MPK, or equal liieats
6. Potentiometer 2K Mallory M2MPK, or equal leary.
7. Relay Potter Brumfield #KR 11AG, or equal 1 ea.
8. Plug amphenol #80 PC2F, or equal 2meake
9. Plug amphenol 80 MC2M 2meak.
10. Cord set Belden 17408-SJ, or equal S Cele
11. Binding post, Superior type DF30 black lear.
12. Binding post, Superior Type DF 30 red meat
13. Aluminum chassis Bud #AC-411, or equal 1 ea.
14. Time switch Tork Hourmaster #4100, or equal 1 ea.
15. Socket amphenol #160-10 Smear
16. Epoxy resin Scotchcast #2 42 lbs.
17. Precision Resistors Wirewound 190 type TX 2212 Precision 125 ea.

Resistor Co. 109 U.S. Highway, Hillside, N.J., (see
Tables I and II).

18. Cable 2-conductor #20 AWG with 2 High-strength steel members. 110 ft.
Neoprene outer sheath. Marsh § Marine Co. Houston, Texas,
Type #TPSC, or equal.

19. Bar solder 50/50 tin-lead for lead sensing tips 6 lbs.
20. Bare copper wire tinned #18 AWG SORE

21. Cable 2-conductor #16. Length as required to connect wave
staff site to recording site.

NOTE: Steel "H' beam is needed for holder for epoxy gage sections.

must be determined locally for each gage. Reversing the two electrical
leads connected to the wave staff will reverse the polarity of the voltage
to the staff, and may aid in changing the electrolytic action, and extend
the periods of operation between cleanings.

The lead sensing tips of the epoxy gage sections are extended from
the main body of the section to increase the insulating distance provided
by the epoxy resin between the sensing tip and the metal gage mount. This
increased distance helps to increase the resistance value of the water
film remaining on the epoxy resin after a wave crest has passed, thus
providing the desired stepped resistance change by the rising and falling
action of the water during wave action.

The penmotor will move in proportion to the stepped resistance changes
in the wave staff, and will provide a profile of the water surface against
time on the moving strip-chart on the recorder.

The series-resistance gage will operate most accurately in locations
where small changes occur in the mineral content of the water. If the
gage is operated during conditions where great changes in mineral content
occur, such as during periods of large snow runoff, the gage calibration
should be checked during such conditions, and the recordings corrected
as necessary.

2. Fabrication of Series-Type, Step-Resistance Gage

Most of the parts needed for fabrication are listed in Table III.
The desired number of epoxy gage sections are molded as shown on Figure 8.
Cables for each section should be long enough to allow submerging all gage
sections at one time while working from the top of the gage mount. This
will allow operating personnel to calibrate the gage at regular intervals.
The top gage section has the lowest resistor value between the top plug
and the second plug. Resistors increase in value from the top of the
gage toward the bottom, the highest value of resistance being between the
bottom plug and the connecting conductor molded into the gage.

The power supply requires the small aluminum chassis and the parts
indicated on Figure 9. Layout of the power supply is not critical, use
of good shop practice is all that is required. The voltage-adjust control
on the constant voltage power module must be available for adjustment.

Three 115-volt receptacle plugs, one line cord and one toggle switch
are installed in the sides of the timer. These items are installed and
wired as shown in Figure 10.

The strip-chart recorder listed in the parts list (Table III) for
this gage has a minimum chart speed of about 12 inches per minute. To
save chart paper, the recorder can be modified for a chart speed of 6
inches per minute. This modification is recommended and is outlined in
Section VIII. A connecting cable to this recorder from its input signal
connector is made in the desired length using 2-conductor No. 18 cable
as shown on Figure 11.

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Clock Motor Winding

Manual Switch
AH&H 20994-BF

Clock Switch

Line Cord
Belden 17408S

Amphenol Plugs
No. 160-10

Ground green conductor in cable and
grounding terminal in amphenol plugs
to timer case.

Figure 10. Programmer for Wave Gages. Plugs and switch to be mounted in
Yight side and bottom of case as mechanically feasible.
(Do not mount on lid.) °

Connector Amphenol Connector Type
80MC2M AN 3108B-14S-6S

2 Conductor, No. |8AWG Cable.
Length as Desired (6-8 ft.)

Figure 11. Signal Input Cable for Strip-Chart Recorder.

The metal wave-gage holder is fabricated to the desired length as
shown in Figure 12; a list of components used in fabrication is shown in
Table IV. Mounting brackets for attaching the holder to the supporting
structure should be strong enough to support the holder during severe wave
conditions. Figure 13 outlines one type of bracket that has been used in
supporting the gage holder on a vertical piling. The gage holder gets two
coats of zinc chromate primer and two or three coats of anti-fouling paint
as used on ship bottoms. Government agencies may use this paint which is
available through Government Services Administration (GSA) supply - Stock
No. GS8010-550-8305 for the primer and Stock No. GS8010-290-6651 for the
anti-fouling paint. DO NOT PAINT THE GROUND ROD. Install the ground rod
after the gage holder has been installed. The holders should be installed
so that about 6 to 8 feet are below mean lower low water, 17 to 19 feet
out of the water.

Only the epoxy wave gage sections that are below or at the water
line require anti-fouling paint. Mold release must be removed from the
gage sections prior to painting. DO NOT PAINT THE LEAD SENSING TIPS.

3. Operation of a Series-Type, Step-Resistance Wave Gage

a. Installation

When placing the epoxy wave gage sections in the gage holder,
the section having the highest value resistors is the bottom section, and
goes into the holder first. The section with the next highest value re-
sistors is placed in the holder on top of this section, and so on until
the section having the lowest value of resistors is in the top of the
gage holder.

The power unit, the strip-chart recorder, program clock, magnetic
tape recorder (if used) and chart rewinder are connected as shown on
Figures 14 and 15.

b. Calibration

The accuracy of the recorded wave heights will depend directly
on the accuracy of the calibration of the gage. There will be enough dif-
ference in each wave gage and in each strip-chart recorded to require that
each gage be individually calibrated.

The ideal calibration would be raising and lowering the gage holder
with the gage sections into the water in small increments and marking the
strip-chart recorder with each move. Usually, lack of water depth, the
manual process required, and the presence of wave action prevent such
calibration.

If many gages are to be calibrated, it may be desirable to provide

a cistern-like basin about 24 inches in diameter with the required depth.
A wave gage holder would be a permanent part of the calibration pit. Such

a pit should be made of concrete pipe or other nonconducting material;
use of a metal wall would cause an inaccurate calibration of the gage.

The procedure outlined below has been satisfactorily used for cali-
bration of staff-type gages. If feasible, a time of low-wave action
should be selected for the calibration.

If possible, the sections that are to be removed from the water first
are kept inside the steel gage holder. This provides a more accurate gage
calibration. If the water is deep enough, place two or three of the sec-
tions in the holder in the order that they are used in the gage. The
section having the lowest value of resistors is on top, and the succeed-
ing sections are below it. When the section having the lowest value of
resistors has been removed from the holder (in the desired calibration
increments), the other gage sections in the holder should be removed, and
a succeeding section should be put in the bottom of the mount, thus all
sections having the lowest resistors will be removed from inside the gage
holder in succession during the calibration process.

Calibration of the gage proceeds as follows:

a) If a magnetic tape recorder is used, calibrate it with
the strip-chart recorder as outlined in Section VII.

b) > Turn thevstrip-chart recorder )!'on-of££!! switch) to, oft":

c) Turn the "off-on" power switch on the power supply unit
Cop on:

d) Remove all epoxy wave gage sections from the metal gage
holder.

e) Turn on the strip-chart recorder using the switches on
the recorder and on the programmer.

f) Using the mechanical lever on the recorder penmotor, adjust
the recording pen to the left side of the chart paper.

g) Place the epoxy gage sections under water being careful to
keep the lead tips adjacent to the metal gage holder with
about the same spacing from the ground rod as they would
have been installed in the gage holder.

h) Adjust the calibration resistor on the power unit to
provide full-scale reading on the strip-chart recorder.

i) Remove all wave gage sections from the water.

j) Repeat steps f, g, h, and i until zero and full scale are

obtained.
Text resumes on page 27

TABLE IV

LIST OF COMPONENTS FOR WAVE-GAGE HOLDER (FIVE-SECTION, 25-FOOT GAGE)

1. Steel '"'H" Beam 4'' x 4" WF-13 pounds per foot, 25 feet long 1 each
2. Steel rod 1/2" diameter 25 feet long, hot rolled 5
Sear Steelsrod) 3/8unx W/2 25) feet) long, hot rolled Dee NN
Ay) Steel z0d73/ 8x 1/2" 10 feet: long, hoty rolled The SUP
5. Steel rod 1/2" x 1/2'! 20 feet long, hot rolled leet
6. Steel plate 3/8" x 6" 20 feet long, hot rolled Lyre
Up Steels plate /(2U exe 3n 5) Leet long hot, zolled Te 3
8. Steel bar 1" x 3", 7" long, hot rolled ile
9. Steel bar 1" x 2", 4" long, hot rolled dy
10. Cap screws, type 316 stainless steel, 5/8" x 6" long, Oe
11 threads per inch Hex head
11. Cap screw, type 316 stainless steel, 5/8'' x 1 3/4" long BQ)
1] threads per inch Hex head.
i2ee Capescnew,. type Sho sitainiless steely 5/38 x Sol/2" jong 7a
13. Lock washer, type 316 stainless steel for 5/8" bolt 455 i
14. Nuts, type 316 stainless steel, 5/8" regular, 11 threads ANS

per inch, Hex head.

NOTE: Mounted to 8-inch Steel ''H" beam pile as supporting structure.

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W5Vv

TAPE RECORDER

TORK BRUSH
TIMER RECORDER
Note: Wave gage connect as shown

on Figure I5 CHART
REWIND

I5V

TORK
TIMER

Figure 14. Diagram of Fresh-Water Staff Gage.

To Power Supply ( black binding post)

No. 14 or 16 AWG Cable between gage site
and recording equipment.

White

To Power Supply (red binding post)

White

Figure 15. Wiring Diagram for
Fresh-water gage section.

Ground Rod

k) Place all gage sections in water and remove the top gage
section from the water 1 foot at a time, and mark the
strip-chart accordingly. Continue with the remaining
gage sections.

1) Check the strip-chart record for linearity.

m) If the chart is not linear, change the voltage out of the
d.c. power module to 52 volts.

n) Repeat steps g, h, i, j, k, and 1. A change in linearity
should be found in the strip-chart recording. If linearity
has improved, continue increasing the voltage in small in-
crements and repeating steps g, h, i, j, k, and 1 until the
desired linearity is obtained. If the linearity is worse,
reduce the voltage in small increments and proceed with
steps g, h, i, j, k, and 1 until good linearity is obtained.

o) Turn off the strip-chart recorder using the switch on the
programmer.

p) Set the programmer to the desired recording program using
screws in the program dial to provide a recording beginning
at the selected hour or hours and for the selected number
of minutes.

q) Place the epoxy gage sections in the metal holder.
r) Place magnetic tape recorder in operation.
s) Gage is now in operation.
c. Maintenance
Maintenance of the gage involves changing the paper chart,
refilling the ink reservoir, and checking the program units for proper

timekeeping.

The epoxy gage sections and the metal holder will require cleaning;
frequency of cleaning will depend on local conditions.

The lead tips on the epoxy sections will possibly grow a covering
that looks like a hard powder. This covering will affect the gage
accuracy and must be removed; use of sandpaper or steel wool may be re-
quired. Reversal of the leads connecting the gage sections to the power
supply sometimes changes the rate of covering, and may be tried if desired.

Servicing of the recorders and programmers should follow instructions
in the manufacturer's manuals.

Section III. PARALLEL-TYPE, STEP-RESISTANCE GAGE FOR SALT WATER

1. Theory of Operation of Parallel-type, Step-Resistance Gage

Due to the low resistance path created by a film of salt water
on the epoxy wave gage sections, the gage design for fresh water cannot be
used in the ocean. To compensate for the low-resistance, salt-water film
and the increased electrolytic action in salt water, it is necessary to
provide low resistance values in the wave staff and to use alternating
current and low voltage in the sensing circuit. The circuit in Figure 16
was evolved to permit the use of low-voltage, low-value resistors, and
alternating current in the wave-sensing circuit. Analysis of this circuit
(Figures 16 and 17) shows that a standard 115-volt, 60-cycle line is con-
nected to a constant-voltage transformer. The output of the transformer
is a constant 115 volts + 1 percent for powerline variations between 95 and
130 volts. This removes variations in the record that might be caused by
a change in line voltage. Output of the constant-voltage transformer is
applied to an autotransformer which provides a means for varying the volt-
age applied to the wave-gage circuity. This feature of voltage adjustment
permits calibrating the wave gage for full-scale indication on the strip-
chart recorder. A voltmeter is used to monitor the voltage out of the
autotransformer.

The selected voltage from the autotransformer is connected to a
stepdown transformer which further reduces the line voltage to a value
suitable for wave-sensing resistors. The stepdown transformer also
isolates the powerline from the wave staff. The secondary winding of the
stepdown transformer is connected in series with the variable-resistance
circuit provided by the parallel-resistor, water-conducting path, and the
primary winding of a step-up transformer. The step-up transformer is
identical to the stepdown transformer except that its windings are used
in a reverse manner.

Output voltage from the step-up transformer is applied to a bridge
rectifier and low-pass filter to convert the varying amplitude (caused
by changes in water level) of the 60-cycle a.c. source to a d.c. signal
suitable for driving the recorder penmotor. The stepdown, step-up trans-
former units and the rectifier-filter unit have fixed resistors incorpor-
ated in them to aid in getting a linear signal from these units.

This circuit utilizing the parallel resistance circuit of the wave
staff and the low-voltage windings of the stepdown, step-up transformers
is a low-voltage, current-sensitive circuit. Such a circuit must have
low resistance electrical connections. It is mandatory that the step-up,
stepdown transformers be placed physically close to each other and as
near as possible to the wave gage staff sections.

Design experience has evolved the resistor values for gages of 20 and
25 feet as listed in Table V. These values operate with the other elec-
trical components listed in Table VI, and should provide a gage with good
operational features and good linearity. Changes in components or re-
sistor values may cause nonlinear gage response, and require circuit
modifications.

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TABLE V

RESISTOR VALUES FOR SALT-WATER PARALLEL STEP-RESISTANCE WAVE GAGE

18.
20.
BA
24.
26.
Zor
So
33.
35.
38.
40.
43.
45.
47.
50.
Seis
55.
58.
62.
65.

For 20-foot gage

3 Ohms

4
6
7
9
0
2
4
6
(0)
2
1
4
6
3
9
6
8
1
8

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Section

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each

TABLE VI

COMPONENTS FOR FIVE-SECTION 25-FOOT PARALLEL RESISTANCE GAGE FOR SALT WATER

1. Programmer, Tork Hourmaster Model 4100 1 ea.

2. Voltage Regulator, Sola Type 20-13-030-1 1 ea.
input 95-130 volts, output 118 volts 30 VA.

3. Variable transformer, Superior Electric Co. Model 10B, input ear
120 volts, single phase, 60 cycles output 0-132 volts 2.25 amps.

4, a.c. voltmeter 0-150 volts, Triplett Model 337-S lerear

(3) Filament transformer Thordarson No. T21Fll 6.3 volts c.t.
6 amperes.

Precision Resistors, wire wound, 1% Type TX-2212, manufactured
by Precision Resistor Company, 109 U.S. Highway, Hillside, NJ (O59)

Values shown in Table V.

7. Scotchcast Resin #2, Minnesota Mining & Manufacturing Co. 42 lbs.
@®) Bar Solder, 50% tin, 50% lead. 6 lbs.
9. Wire solid copper, plastic insulation AWG #14 GS) AE

¥ Resistor, 500 Ohms, 10 watt 1 ea.

‘ é) Selenium rectifier, International Rectifier #Q4B, 130V 4 ea.
RMS, 100 MA

Capacitors, Sprague 155 P-156P Metallized-paper Tublar
4.0 mfd. 200 volts.

AG) Filter choke, Stancor C 1721 1 ea.
8.5 Henrys 200 MA»

14. Box-Mounting receptacle Bendix Scinflex, RB 3102 #10-42214-2P leak
Scintilla Division, Bendix Aviation Corp., Sidney, N. Y.

15. Plain Gasket, used with box-mounting receptacle, Bendix 1 ea.
Scinflex #10-40450-14

16. Straight plug, Bendix Scinflex RB-3106 #10-42614-2S with 1 ea.
#10-40908-141 back shell and #10-40457 Hex coupling nut
and #AN-3057-6B cable clamp.

17. Box, aluminum watertight 4 1/2" D x 6 1/2" W x 6 1/2" H 1 ea.
Adalet #JP102, A Adalet Mfg. Co. Cleveland, Ohio.

40.

TABLE VI (continued)

Utility box, metal 5" D x 6'' W x 9" H, Black Crackle 2
finish - Bud #CU 1099B.

Switch SPST, Arrow Hart §& Hegeman #20994BF 1
Chart rewind, Brush Model #RA-2402-11 il
Strip-Chart Recorder Brush Model No. RD-2321-00 (order with 1

following modifications: single channel operation and 50 mm
chart width. Old style penmotor #BL 902 and Long Pen #BL 921.

Wire solid copper, bare, tinned, AWG #18 50

Cable 2-conductor #20 AWG with 2 high-strength 1 1/6" steel 110
members. Neoprene outer sheath Marsh and Marine Mfg. Co.,
Houston, Texas, Type #TPSC.

4-conductor #14 AWG rubber covered. Length required to
connect wave staff site to recording site.

Plug amphenol #160-10 3
Line cord a.c. Belden 17408-S

Resistor, 11 Ohms 1% tolerance 10 watts IRC #AS-10
Connector, male cable plug Amphenol type #80-MC2M

Connector, female receptacle, Amphenol type #80 PC2F 2
Relay DPDT, 115 volt, 60 cycles Potter Brumfield KRP 11AG 1
Potentiometer 2K-Ohms Mallory M2MPK, or equal 1
Solder, 18 S.W.G. 60% tin/ 40% lead i
Socket, Octal, Amphenol #78RS8 1
Connector, female 3-wire polarized type Harvey Hubbell 1
"Twist Lock" #7484.

Connector, male base 3-wire polarized type Hubbell #7486 1
Connector, male cap, 3-wire polarized type Hubbell #7485 1
Connector, female base, 3-wire polarized type Hubbell #7487 1
Cable, electrical, rubber covered, three-conductor AWG #18 15
Belden type 8453

Cord - Grip for rubber covered cable 0.500 - 0.625 diameter. 1
aluminum, Pyle-National #DB-10

Cable 2-conductor #18 AWG Belden #8452, or equal 2

NOTE: This list does not include gage mount.

ea.

ea,

ft.
fates

ea.

Pitre

The gage will operate in salt-water locations that have little or no
change in salinity. If the gage is placed in locations having significant
salinity changes, the wave record will vary in accuracy with the changes
in salinity.

2. Fabrication of a Parallel Step-Resistance Gage

Fabricate the required number of 5-foot epoxy gage sections as
outlined in Figure 18. The top gage section will have the lower value
resistor connected to the top five sensing plugs, and the resistors will
progressively go higher in value until the highest value of resistors are
connected to the five sensing plugs, and the resistors will progressively
go higher in value until the highest value of resistors are connected to
the five sensing plugs on the bottom gage section. The cable from each
wave gage section (molded as part of the section) should not extend more
than 10 feet from the top of the gage mount. The resistance in the gage
cables and leads from the transformer unit connected to the gage cables
and leads from the transformer unit connected to the gage cables are part
of a low-voltage, current-sensitive circuit. The resistance of these
connections must therefore be low; long leads or high resistance con-
nections in this circuit must be avoided in order to provide best gage
linearity. Wire size in the cables molded into the gage sections should
not be smaller than 2-conductor No. 20 AWG in parallel.

Fabricate the transformer unit as shown on Figure 19. Wire the
transformer unit as shown on Figure 20. Be sure that all connections in
this unit are well made and well soldered. This unit may be filled with
a clear potting compound available from Dow Corning Company, their No. 182.
If this unit is not filled, care should be taken to ensure that it is
watertight.

Fabricate the voltage control, rectifier-filter unit, and programmer
as shown on Figures 10 and 21 and wire as shown on Figures 10 and 22.

Strip-chart recorder chart speed may be modified, if desired, as
outlined in Section VIII. Fabricate the signal connecting cable for
the strip-chart recorder to the desired length using 2-conductor No. 18
AWG cable as shown on Figure 11.

Fabricate the metal gage holder to the required length shown in
Figure 12. Suitable mounting brackets for the gage holder should meet
local installation requirements. Mounting brackets must be strong enough
to withstand the forces of wave action expected at the gage site. A
bracket design that has been used on vertical piling is shown on Figure
13 which may serve as a guide.

Paint the gage holder with two coats of primer and two coats of any
good commercial anti-fouling paint. Government agencies may use Government
Services Administration GSA Stock No. GS8010-550-8305 and GS8010-290-6651,
respectively. DO NOT PAINT THE GROUND ROD. Paint the gage sections that
are below and at the water line with three coats of anti-fouling paint.
Clean the sections of mold release prior to painting. DO NOT PAINT THE
LEAD SENSING TIPS.

Text resumes on page 40

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3. Operation of Parallel-type, Step-Resistance Gage

a. Installation

Install the metal gage holder at the operation site. The
holder should be installed so that about 6 to 8 feet are below mean lower
low water and 17 to 19 feet out of the water.

Provide a mounting for the transformer unit near the top of the gage
mount but do not mount the transformer unit at this time.

Install the 4-conductor No. 14 AWG cable between the gage holder site
and the recorder site.

Install the epoxy gage sections in the mount.

Install the voltage-control programmer unit, the strip-chart recorder,
chart take-up and magnetic tape recorder (if used) at their operating site.
Connect these units and the transformer unit to the gage sections as shown
on Figures 23 and 24.

b. Calibration

The accuracy of the recorded wave heights depends directly on
the accuracy of the calibration of the gage. There are enough differences
in each wave gage and each strip-chart recorder to require that each gage
be individually calibrated.

The ideal calibration would be that of raising and lowering the steel
gage holder with the gage sections into the water in small increments and
marking the strip-chart recorder accordingly. Usually, the lack of water
depth, the manual process required, and the presence of wave action prevent
such calibration.

If many gages are to be calibrated, it may be desirable to provide a
water basin about 24 inches in diameter with the required depth. A wave
gage holder would be a permanent part of the calibration pit. The basin
should be made of concrete pipe or other nonconducting material; use of
a metal wall would cause inaccurate calibration of the gage. Water with
proper salinity would be required.

The procedure outlined below has been used and found satisfactory for
calibration of staff-type gages. If feasible, a time of low wave action
should be selected.

If possible, keep the sections to be removed from the water first in
the calibration process inside the steel gage holder. This will provide
a more accurate gage calibration. If the water is deep enough, place two
or three of the sections in the holder in the order that they are used in
the gage. The section having the lowest value of resistors is on top, and

TRANSFORMER
UNIT

(See Fig. 23)

O
Z 4 conductor No. 14 or No.I6
— gage cable to recording
A O equipment.
O
Keep these cables in as short
= length as practicable.
B ES
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Figure 23. Connecting Diagram for Parallel Step-Resistance Gage Section

POWER UNIT PARALLEL WAVE GAGE

115 Volt Line

RSs een ais A Name aa Na a aR eR a a ar a a eT: Ia oe =]
1 |
1 |
To Transformer Unit
| |
|
|
|
VARIABLE
| I
| RECTIFIER UNIT CRANSEGRUIER 1
| |
| |
| |
! |
y |
| |
| 1
| |
| |
y |
y |
| |
| |
CONSTANT- |
PROGRAMMER VOLTAGE
TRANSFORMER
| |
| |
| |
| |
a

4 Conductor Cable Gp

To 115 Volt Power Line

STRIP-CHART MAGNETIC TAPE
RECORDER RECORDER

BRUSH MODEL
RD-2321-00 ee eae
( Modified)

ABCD

TRANSFORMER
UNIT

(Sce Figure 26)

CHART REWIND

BRUSH MODEL PROGRAMMER Short Cable to Gage
RD-2402-1|
( See Figure 23)

Figure 24. Hookup Diagram for Parallel-type Step-Resistance Gage.

the succeeding sections are below it. When the section having the lowest
value of resistors has been removed from the holder (in the desired cali-
bration increments), the other gage sections in the holder should be
removed and a succeeding section put in the bottom; thus, all sections
having the lowest resistors will be removed from inside the gage mount

in succession during the calibration process.

Calibration of the gage proceeds as follows:

JS)
k)

If a magnetic tape recorder is used, calibrate it with the
strip-chart recorder as outlined on page 93.

Remove the epoxy gage sections from the gage mount.

Set the a.c. voltage-adjust control (autotransformer) on the
voltage-control, rectifier-filter, programmer unit to its
counterclockwise position.

Apply power to the gage system and turn on the strip-chart
recorder.

Using the mechanical adjusting lever on the strip-chart recorder
penmotor, adjust the recording pen to the left side of the
recording chart.

Place all epoxy gage sections under water. The sections should
be placed adjacent to the metal gage holder with the lead contact
tips near the ground rod. The spacing between the tips and the
ground rod should be nearly the same as that provided when the
sections are inside the gage holder.

Adjust the a.c. voltage control clockwise to provide full-scale
movement of the strip-chart recorder pen.

Repeat steps b, e, f, and g until zero and full-scale are stable.

Remove the top epoxy gage section from the water 1 foot at a
time, and mark the strip-chart recording accordingly. Continue
with the remaining gage sections. This is the calibration for
the wave gage. If the calibration is nonlinear, clean the lead
contact tips on the gage sections, check the electrical con-
nections of the epoxy gage cables and the connection to the
ground rod, and recalibrate.

Mount the transformer unit near the top of the gage holder.

Adjust the programmer to provide the desired recording periods
of the wave gage. The programmer may be set to provide a re-
cording beginning any hour for a selected number of minutes.
Hours may be skipped by proper installation of the knurled
screws in the programmer dial.

1) Place the epoxy gage sections in the gage holder.

m) Gage is now in operation.

c. Maintenance

The gage sections and mount will require cleaning as dictated
by local marine growth conditions.

Repainting the gage mount and the lower epoxy sections with anti-
fouling paint will extend the periods between cleaning. DO NOT PAINT
THE GROUND ROD AND THE LEAD TIPS IN THE EPOXY GAGE SECTIONS.

Recording charts and ink will require replacement at intervals in
proportion to the recording program selected.

SECTION IV. RELAY-TYPE STEP-RESISTANCE GAGE FOR SALT AND FRESH WATER

1. Theory of Operation of a Relay-Type Step-Resistance Gage

The CERC relay-type step-resistance gage is designed for opera-
tion where water salinity is expected to vary widely. This variation may
approach that of fresh water or that of sea water with little change in
gage operation. This gage holds calibration longer than other staff gages.

The gage operates on the principle of water completing a circuit
consisting of a power supply, a relay coil, and a switch (the switch is
the water path) in series (see Figure 25 on the following page).

The gage uses 125 relays for a 25-foot gage, each relay closing when
its associated water contact is submerged. Only one power supply is
required to operate all the relays.

In order that the relays will operate in both fresh and salt water,
it is necessary to modify the basic circuit in Figure 25 to the circuit
in Figure 26.

Electrolytic action in the water path makes it necessary to use
alternating current in the gage circuit. However, when an a.c. relay is
used, excessive relay chatter shortens relay life. This limitation makes
it necessary to select a d.c.-operated relay, and subsequent selection of
suitable rectifiers and filters for converting the a.c. gage-circuit
potential to d.c. for relay operation.

The basic relay circuit requires approximately 18 volts for operation
in fresh water. When the same voltage is applied to the gage circuit in
salt water, the voltage across the relay coil exceeds the coil voltage
rating. To overcome the relay-coil overload, a 28-volt .07 ampere pilot
lamp is installed to provide relay protection in salt water. In addition,
this lamp will have a lower resistance value when not fully excited, thereby
providing a correspondingly higher voltage to the relay coil when used in
fresh water.

The relays are connected to the copper contacts on the epoxy gage
sections so that when the bottom contact on the gage is submerged, relay
No. 125 is first to close, and when all contacts are successively submerged,
relay No. 1 will be the last to close.

The a.c. power-supply voltage to the relay circuit is adjustable by
changing a jumper wire on a terminal strip on the power-supply chassis.
The voltage should be adjusted to the minimum value that will provide
positive relay closure at the location of the gage. For sea water, 9 to
12 volts should be adequate; for most fresh water locations, 18 to 24
volts should be adequate.

Relay

Water Contact
Ground Rod

in Water

Water Surface
Power

Figure 25. Simplified diagram of relay-type, step~resistance gage.

@ dng arin
Silicon Rectifier
: 5 INI692

28 Volt — .O7 amp. lamp

Relay 1100 ohms

1/2 watt

Pull in 5 volts
6MA+ IMA

Drop out above 35
ampere turns

6 to 24 V. adjustable Water Contact

Gage Ground
Rod ~“~s~a_|

Water Surface
115 Volt

60 Cycle

Figure 26. Modified circuit for relay-type, step-resistance gage.

Gage response (relay response) to a rising water surface is prac~
tically instantaneous. Gage response to a falling water surface is
directly affected by the water salinity and cleanness of the epoxy gage
sections. The epoxy gage sections should be kept as free of sea growth
and dirt as local conditions will permit. Visual observations of wave
action (counting the number of gage contacts from wave crest to trough)
on the staff and comparison with the recorded wave record should provide
evidence of proper gage operation. If local conditions permit, cleaning
the epoxy gage sections and applying a coat of silicone wax to the epoxy
will provide outstanding gage response. (Do not coat the copper contacts.)

In addition to the relay-operating circuit, the gage contains the
step-resistance recorder circuit which provides the signal to the recorder
as dictated by the number of relays activated by the water level.

The circuit in Figure 27 shows that when all relays are in the un-
energized condition (no gage contacts submerged), the step-resistance
circuit is open and no voltage is available to the recorder input. When
the bottom gage-contact is submerged and relay No. 125 operates, all re-
sistors in the step-resistance network are in series with the d.c. power
and recorder input. As each gage contact is submerged and the relays
are operated, the resistors are short-circuited. This provides a higher
voltage to the recorder as each relay closes (voltage to recorder is
higher as the gage is submerged). Thus, the recorder will follow the
change in water submergence of the wave staff.

2. Fabrication of a Relay-Operated Step-Resistance Gage

Fabricate the required number of 5-foot gage sections as required
for the wave station. Table VII is a parts list for a relay-operated gage.
Fabrication details of the sections are shown in Figure 28. Resistor
values and cable color-code are in Table VIII. Cable lengths for the
sections should be selected for the shortest length practicable to reach
the location of the relay cabinet. Cost of the 25-conductor cable used
in the fabrication of the epoxy sections is about $0.50 per foot, thus, a
five-section gage will have a cable cost of $2.50 per foot between the gage
mount and the relay cabinet.

Fabricate the relay panels and relay power supply according to
Figures 29 and 30, and wire them as shown in Figures 31 and 32. Mount
these units in the relay cabinet as shown in Figure 33.

Modify the strip-chart recorder paper speed (if desired) as outlined
on pages

Install three female 115-volt receptacles, one toggle switch anda
line cord in Tork Timer Model 4100 as outlined on Figure 10.

Fabricate a metal gage holder of proper length as shown on Figure 14.
Fabricate gage-holder mounting brackets as local installation requirements

Text resumes on page 59

RECORDER
115 Volts
60 Cycles TIMER

297-94 VOLES
D.C. POWER SUPPLY

(Regulated)

1500 ohms

Resistor
No. | Relay No. |

Resistor
No. 2 : Relay No. 2

: Relay No. 3
: (Controlled by bottom
Relay No. 125 gage-contact )

Figure 27. Simplified Diagram for Relay-Gage

Resistor
No. 124

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ALUMINUM ANGLE PANEL MOUNT

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All holes to clear 6-32 machine screws (No. 28 drill)

(2 holes) No.33 drill to clear 4-40
machine screws, all others to clear
6-32 machine screws (No.28 drill)

PLUG MOUNTING BRACKET

Figure 29. Relay-panel layout for relay-type gage.

_
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te a ices

1-11/64" Dio. hole

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screws (use Tinnerman clips)

3/8" Dio. hole

1/2" Dia. hole

Drill 6 holes for No.6 sheet metal screws

3/8" Dio. hole 1/2" Dio. hole 5/16" Dia. hole

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TABLE VII

COMPONENTS FOR FIVE-SECTION 25-FOOT RELAY STAFF GAGE

Relay assembly consisting of Wabash magnetic coil No. L4988
or equal and Hamlin DRG-1 contact relay, or equal. Relay
contact material is to be silver relay contacts to close

at 3.85 + 0.15 volts and 5.8 + 0.2 milliamperes. Relay
contacts to open at 3.3 + 0.2 milliamperes.

Machine screws steel nickel plated binder head, 6/32 x 1/2"
long.

Hookup wire (Alpha #1500 #24 Standard (any color)
NUESHesteclinackelspiliateds 6/325 x (1/44

Lockwashers, internal teeth #6

Aluminum angle, 1" x 1" x 1/16" thick

Aluminum angle, 1" x 2" x 1/8" thick

Cable, 25-conductor - Marsh and Marine, Houston, Texas
Type XS CG 13R.

Scotchcast Resin #2, Minnesota Mining §& Mfg. Co.

Stainless Steel #316, round rod 1/4" O.D.

Plexiglas sheet 1/4" thick, 36 x 36

Precision Resistors, wire wound 1%, Type TX-2212,
manufactured by Precision Resistor Company, Hillside, N.J.

(See Table V)

Rotary Switch Centralab #PA-2000 1 pole, 2-12 position
shorting type.

Capacitor, Cornell-Dubilier ECSP 50-50

Semiconductor rectifier, GE type 1N1692

Resistor 1,100 Ohm 1/2 watt 5% IRC GBT 1/2
Amphenol plug #26-4301-32 P

Amphenol receptacle #26-4401-32S

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24.

255

26.

Zils

28.

29.

30.

Silks

32.

33.

24.

35.

36.

37.

38.

TABLE VII (continued)

Pilot Lamp #1829-28 V.O. 07 amp.
Pilot Lamp Socket -Dialco #7-87
Aluminum chassis Bud #AC-422, 5" x 13" x 3"

Socket, 6 prong, Amphenol #78S6, with amphenol #3-24
cable clamp

Plug, Amphenol 86-RCP6
Switch, SPST-12 Amps-AH §& H #80607

Panel aluminum, 3 1/2'' H x 19" W, Bud #PA-1103-HG,
Hammertone Gray.

Panel aluminum, 5 1/4" H x 19" W, Bud #PA-1103-HG,
Hammertone Gray.

Cabinet - Panel 26 1/4" H x 19" W, Bud CR-1744 HG
Hammertone Gray.

Relay DPDT 115 v. 60 cycles Potter Brumfield KRP11AG

Timer Tork Hourmaster #4100

Cable, 2-conductor stranded, AWG #18 Type SV, Belden 8452

Cable, 5-conductor stranded, 3-AWG 20, 2-AWG 18, Belden 8455

Binding post, G.C. Electrocraft 33-270B
Transformer, Stancor #P6429

Solder, 18 S.W.G. 60% tin/40% lead

Clip #UMC-10 Sprague Products Co.

Wire, copper, solid-tinned AWG #18
Potentiometer, 1,500 Ohms Mallory M1.5MPK

Terminal Block, H. H. Smith #602-5, General Purpose
Bakelite.

ea.

Ca.

ea.

€a.

ea.

ft.

fats

ea.

1b.

ea.

fit.

ea.

39.

40.

41.

42.

43.

44,

45.

46.

47.

48.

NOTE:

TABLE VII (continued)

Shaft lock H. H. Smith #181

Female Chassis receptacle amphenol #80-PC2F
Male cable plug amphenol #80-MC2M

Cord Belden #17460-S

Plug amphenol #86CP8 with #324 cable clamp

d.c. Power supply output volts 29.2 - 32.7, output current
0.050 amps accuracy + 0.05% Model M-31.5-050A, manufactured

by Technipower, Inc. 18 Marshall Street, South Norwalk, Conn.,
Rep. Whitcomb Associates, 730 Deepdene Road, Baltimore, Md.

Plug amphenol #160-5

Potentiometer, 2,000 Ohms, Mallory M2MPK

Strip-Chart Recorder Brush Model No. RD-2321-00. Order with
following modifications: Single channel operation and 50 mm

chart width. Old style Penmotor #BL902 and Long pen #BL 921.

Chart take up drive Brush No. RA 2402-10

Less steel "'H'' Beam for holding epoxy gage sections.

ea.

Ca.

ea.

Ca.

ea.

Ca.

€a.

NWOUrFOArPAOHRFrFONNONFRFPODANONMN

TABLE VIII

RESISTOR VALUES IN OHMS FOR 125-POINT RELAY GAGE

Brown
Red

Brown
Clear

Red
Orange

Red
Yellow

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9 Red
10 Green

11 Red
12 Blue

13 Red
14 White

15 Red
16 Clear

17 Orange
18 Clear

ioe)
88.0
92.7
96.7
101.
106.
110.
116.
12
NAA s
134.
141.
149.
LSG
166.
7.6.
186.
198.
Zales
Dede
240.
PST
2710.
298.
322.

CABLE-COLOR CODE FOR RELAY GAGES

348
379
413
452
498
550
611
683
768
871
995
1149
1340
1584
1900
2323
2901
3733
4977
5968
10453
17423
34817
104500

Yellow
Clear

Green
Clear

Blue
Clear

White

Clear

(spare
Conductor)

dictate. Brackets should be designed with adequate strength to support
the gage holder during severe wave action. Figure 13 shows a type bracket
that has been used successfully to support the gage holder on a vertical
piling. Paint the gage holder and mounting brackets with two coats
primer and three coats of a good grade commercial anti-fouling paint.
Government agencies may obtain these from General Services Administration
Stock No. GS8010-550-8305 and GSA Stock No. GS8010-290-6651, respectively.
Paint the underwater and waterline epoxy gage sections with three coats
of anti-fouling paint. DO NOT PAINT COPPER SENSING TIPS.

3. Operation of Relay Type Step-Resistance Gage

a. Installation

Install the gage holder at the operating site. The holder
should be installed so that about 6 to 8 feet are below mean lower low
water and 17 to 19 feet out of the water. Install ground rod in holder.
DO NOT PAINT GROUND ROD.

Place epoxy gage sections in gage holder.

Install relay cabinet, strip-chart recorder, chart rewind, programmer
and magnetic tape recorder (if used) in operating location.

Connect all units of the system as shown on Figure 34.

Adjust tape recorder (if used) and strip-chart recorder as outlined in
Section VII, paragraph 3.

b. Calibration
Calibrate the gage as follows:

a) Apply power to the relay cabinet. Adjust the d.c.
voltage from the regulated d.c. power module to 30.0
volts. Turn on the strip-chart recorder, using the
toggle switches located on the programmer and rear of
recorder.

b) Place the toggle switch on the relay cabinet marked
"calibrate-operate' to the "calibrate" position.

c) Place the rotary switch on the relay cabinet to the
"operate" position.

d) Adjust the strip-chart recorder pen to the left side

of the chart paper using the lever on the side of the
recorder penmotor.

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Place the rotary switch on the relay cabinet to posi-
tion 5 (full-scale setting).

Adjust the linearity control on the front panel to the
relay cabinet to provide full-scale pen movement on the
strip-chart recorder.

Move the rotary switch to its intermediate calibrate
positions and mark strip-chart recorder accordingly.

Check strip-chart recorder for linearity. If recording

is not linear, adjust d.c. voltage of the regulated power

module either up or down and repeat steps e, f, g, and
h until linearity is obtained.

Place rotary switch in "operate" position.

Place the toggle switch marked "'calibrate-operate" to
the "operate" position.

Raise or lower the epoxy gage sections in the water,
and observe the strip-chart recording for a correspond-
ing indication.

A relay that is stuck closed will cause the recorder
pen to remain at an up-scale position when all gage
sections are removed from the water. A relay that
does not close will be indicated by a jump in the
recorder pen as the gage sections are lowered into

the water. The terminal strip on the rear of the
power-supply unit allows for adjustment of the voltage
applied to the relay circuit. Salt-water locations
require 9 to 12 volts for normal operations. Set
voltage to the lowest value that will provide positive
relay action and best relay fallout when the gage sec-
tions are raised and lowered in the mount. A d.c.
voltmeter may be used to measure the d.c. voltage
across a relay coil that is in a closed position; this
voltage should be about 5.5 to 6.5 volts. Greater
relay voltage will cause the relays to remain closed
when the gage sections are saturated with water, but
with the gage contact out of water. This is due to
conductivity of water film on the gage section.
Excessive voltage will cause capacitor failure in

the relay circuit.

Adjust programmer to time recordings from the gage as

desired. The programmer will provide a recording at
the beginning of each hour for the selected number of

minutes. Hourly recordings may be deleted for any
period by removing the knurled screws from the
programmer dial.

m) Gage is now in operation.

c. Maintenance

Recorder chart and ink must be replaced in accordance with
the recording program established.

The epoxy gage sections, gage holder, and brackets will require
periodic cleaning to remove sea growth caused by local conditions.
Repainting of the gage holder and gage sections with anti-fouling paint
will extend the periods of operation between cleaning, and retard marine
growth. DO NOT PAINT THE GROUND ROD OR THE METAL GAGE TIPS.

Recorders should be serviced as outlined in the manufacturer's
manuals.

Periodic checking of the gage calibration is desirable.

Section V. PRESSURE-SENSITIVE GAGE

1. Theory of Operation of Pressure-Sensitive Gage

The pressure-sensitive wave gage operates on the principle that
when a wave crest passes a given point there will be an increase in water
depth, and with an increase in the height of the water column there will
be an increase in the pressure at the bottom of the colum.

While a wave crest is not exactly equivalent to closed water column,
the change in water level related to a wave crest or trough will cause a
pressure change at the ocean bottom. If a pressure-sensitive device is
placed near the ocean bottom, it will sense the pressure change caused
by the wave.

The signal from the pressure-sensitive device may be carried to a
shore location over an electrical cable, and recorded on a paper-strip
chart or magnetic tape recorder. Since the signal at the recorder is
produced by the wave crest and trough, it is directly related to the wave.

The pressure change produced by a wave train of constant amplitude
and constant period will decrease as the pressure sensor is placed deeper
and deeper in the water. If the wave period is made shorter, the pressure
from the same wave height will also be reduced at a constant water depth.
Ratios for conditions of pressure, depth, wave height and wave period
have been established, and may be used to correct the recordings from a
pressure-sensitive wave gage to provide a usable measurement of wave
conditions.

Ripples and small sharp surface changes will be filtered out of the
wave record due to the pressure-period attenuation outlined above. This
filtering will influence the wave spectra analysis so that there will be
apparent differences when comparing spectra data taken at the same time
and location with both pressure and staff gages.

The change in tide at locations where pressure wave gages are used
must be known. The increased water depths due to tide is, in effect, an
increase in water depth, which must be used in correcting the wave record.

For these reasons a pressure-sensitive gage is not an ideal device
for gathering true data on waves. This gage is recommended only for those
locations where the installation of a step-resistant staff-type gage is
impracticable due to the cost of a mounting structure or where a mounting
structure would cause a navigational hazard.

The CERC-designed pressure-sensitive gage uses a Sylphon bellows
that changes its length with an increase in pressure. The bellows move-
ment is coupled to the core of a linear differential transformer by a
permanent magnetic, steel ball, universal joint.

Movement of the core in the differential transformer produces a
linear d.c. output voltage from the unit. This signal, representing the
wave conditions, is amplified and applied to a strip-chart recorder.

2. Fabrication of a Pressure-Sensitive Gage

Fabricate the pressure-sensitive underwater unit as outlined on
Figure 35. Table IX is a parts list for this gage. When soldering the
end caps to the bellows, ensure that a watertight seal is provided and
also prevent any solder from entering the corrugations of the bellows.
The end for the bellows which is drilled for the magnet should be soldered
to the bellows first. The magnet should then be inserted using an epoxy
cement to ensure that it remains in place. The threaded end for the
bellows is then assembled (soldered) using the minimum heat required for
soldering. Too much heat could lower the efficiency of the magnet. It is
recommended that edges of the bellows and the end caps be tinned prior to
soldering into an assembly. It is also recommended that liquid stainless
steel flux and solid wire solder, 60 percent tin and 40 percent lead, be
used.

When assembling the bellows unit to the main gage housing, use of
Permatex No. 2 on threaded surfaces is recommended. The Permatex should
be used sparingly, applying only a thin coat on both the male and female
threaded parts. Prior to closing the space between the bellows and gage
housing, remove any excess Permatex from inside the "0" ring; align the
brass ring, which incloses the ''0'' ring, with the outside gage housing
and tighten the housing firmly. Do not use the bellows as a purchase
grip to tighten the assembly; vise grip pliers and a bench vise are
recommended.

The bellows should be assembled to the gage case, and the entire case
and bellows tested for leaks prior to further assembly. This can be done
by attaching a fitting to the cable end of the gage housing, filling the
inside with air to about 30 pounds per square inch gage, and testing under
water for bubbles. During this test, the bellows snould be blocked mechan-
ically to prevent stress beyond its ratings. Blocking may be accomplished
by using large plastic washers with small holes in their edges for accept-
ing wire to hold the bellows in a blocked position. The washer used on
the threaded end of the bellows will require a slot with an opening in
order to place it above the bellows cap as shown in Figure 36.

After testing the bellows and housing assembly, a short length of
gage cable is fitted into the end of the gage housing and sealed with
epoxy resin. Splicing the cable ends to a very fine flexible wire in the
epoxy seal will aid later assembly of the transducer. Clean, but do not
oil, the sliding core in the Sanborn linear differential transformer.
Clean the core and center hole thoroughly. If the core does not slide
freely in the transformer, return the transformer and core to the manu-
facturer for repair or replacement. Any binding of the core will cause
it to separate the steel ball from the magnet and render the gage useless.
The steel ball and magnet provide a backlash-free universal joint that
allows free movement of the core within the transformer. The core

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TABLE IX

LIST OF COMPONENTS FOR PRESSURE-SENSITIVE GAGE, MODEL BE-2

Brass parts and magnet as shown on drawing, ''Pressure Wave
Gage Model BE-2.

Bellows, 2-ply brass, 10 active corrugations, reference line
No. 2137, Robertshaw-Fulton Controls Co., Fulton Sylphon
Division, Knoxville, Tennessee.

Transducer, d.c. differential transformer displacement, DCDT,
Model 7DCDT-500, Sanborn Company, Transducer Division,

‘Waltham, Massachusetts.

Amplifier, Transistorized operational, Model TR-1 with mating
amphenol connector suitable for chassis mounting, Boonshaft

& Fuchs, Inc., Hatboro Industrial Park, Hatboro, Pennsylvania.

Power supply, dual-output regulated, 60 volts d.c. Model

60B10D-60B10D, Acopian Technical Company, Easton, Pennsylvania.

Power supply, regulated-output 6.0 volts d.c., 0.375 amperes
d.c. Model M-6.0-0.375A, Technipower, Inc., South Norwalk,
Connecticut.

Socket, Amphenol, 11 prong #78S11

Chassis, aluminum 6" x 17" x 3", Bud AC-433

Splicing kit, Scotchcast #82-Al

Cord Set Belden 17408-SJ

Connector, male cable plug, amphenol type #80-MC2M
Connector, female receptacle, amphenol type 80PC2F

Socket, octal, amphenol #78RS8

Capacitor, Mallory, No. HC10100, 10,000 MFD 10VSP

Plug, 3-prong, male with shell, amphenol #160-5

Cord Set, Belden 17460-S

Switch, toggle SPST, Arrow Hart §& Hegeman #20994-BF

Socket, 3-prong female chassis mounting type amphenol
#160-10

l set

1 ea.

2 ea.

1 ea.

I ear.

1 ea.

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3 ea.

NE).

20.

Blk

C26

23.

24.

25.

26.

ilk

28.

ZS)

30.

Sho

34.

TABLE IX (continued)
Time switch, Tork #4100
Potentiometer, 10-turn, 200 K ohms, IRC type HD-150
"Revodex'' dial, IRC type RD-462
Relay DPDT, 115-volt, 60 cycles, Potter Brumfield KRG 11AT
Binding Post, Superior type DF 30 GNC (Green)
Binding Post, Superior type DF 30 WTC (White)
Binding Post, Superior type DF 30 BC (Black)
Binding Post, Superior type DF 30 RC (Red)
Capacitor, .047 MFD, 200 WVDC, Cornell-Dubilier Type WMF 2S47
Potentiometer 2,000 Ohms Mallory #M2MPK
Nameplate, Brass
Solder, 18 S.W.G. 60% tin/40% lead
Resistor, 2,700 Ohms, wire wound, 1 watt, 5% tolerance
Material for Concrete mounting block
Strip-chart recorder, Brush #2321-00. Order with following
modifications: single channel operation and 50 mm chart

width. Old style penmotor #BL 902 and long pen BL 921.

Chart rewind Brush #RA-2402-10

ea.

€a.

Ca.

ea.

1b.

ea.

€a.

ea.

1/8" Dia. hole

I- 3/16" R.
Plexiglass 1/4" thick

TOP WASHER

1/8" Dia. hole

BOTTOM WASHER

Figure 36. Washers for blocking bellows of pressure gage.

assembly should be placed in the linear differential transformer and
placed in the gage barrel. Plastic washers must be placed between the
transformer and the bottom of the barrel. These washers must be of
varying thicknesses. The electrical output of the transformer should
be zero or slightly negative when the transformer is resting on the
washers in the gage barrel.

Connect the differential transformer to a 6-volt d.c. source and
measure the output with a high-impedence voltmeter set on a low range -
about 3 volts. With the steel ball in contact with the magnet in the
bellows chamber, with the bellows in free air (no pressure), and the
transformer in firm contact with the plastic washers, the voltmeter
should read 0 volts, or slightly negative. Pressing the bellows with
the fingers should show an upscale (positive) movement of the voltmeter.
If the zero or slightly negative output voltage is not obtained on first
trial, then the transformer and core assembly must be removed from the
gage barrel and plastic washers of a different thickness tried until the
correct reading is obtained. After the correct washers are selected,
put together the spring assembly and ''0" ring, and solder the transformer
leads to the leads in the epoxy sealed cable-end of the gage housing.
Fasten the cable portion of the gage housing to the gage barrel, using
6 No. 10-32 screws. These screws should be tightened a little at a time
to ensure equal pressure on all sides of the "0" ring seal.

Fabricate the amplifier, power-supply unit as shown in Figure 37;
wire the unit according to Figure 38.

Construct the programmer by installing three 115-volt receptables,
toggle switch and line cord on the timer as shown on Figure 10.

Change the chart speed on the strip-chart recorder (if desired) as
outlined in Section VIII.

Fabricate a signal cable for the strip-chart recorder of the desired
length using 2-conductor No. 18 AWG cable and connectors as shown on
Figure 11.

Fabricate a suitable underwater mount for the pressure unit. This
mount should be high enough to keep the gage free of the ocean bottom;
it should be large enough and heavy enough to remain in an upright posi-
tion during periods of heavy wave conditions. To prevent metal erosion
caused by galvanic action, dissimilar metals should not be used in contact
in sea water. The brass pressure-unit must be mounted in plastic insulat-
ing brackets to prevent metal erosion by galvanic action. Lifting eyes
should be provided to lower the mount to the ocean floor and for attaching
a marker buoy (if required). A simple concrete mount has been used for
the gage in some locations (Figure 39). If a marker buoy is used, the
gage should be protected from the sagging and twisting of the buoy cable.

TAPE BRUSH
PROGRAMMED LINE CORD RECORDER RECORDER
A.C.

“
=
a

Tip jacks for setting 60 volt Binding posts for

power supply voltages gage cables
a
WZ

Potter Brumfield
Relay

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yy

DUAL 60 VOLT
ACOPIAN POWER BOONSHAFT and FUCHS
SUPPLY TECHNIPOWER AMPLIFIER

POWER SUPPLY

TOP VIEW

FRONT PANEL

TIDE CAPACITOR
POWER SWITCH AMPLIFIER GAIN SWITCH

Figure 37. Power Supply Unit for amplifier of pressure-sensitive gage.

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Wave Gage Cable

Gage Mounting Bracket

1" Dia. Brass or Steel Rod

Metal Lifting Ring, 3/4" Steel Rod

E ee ee

Figure 39. Concrete Block for Mounting Pressure-Sensitive Gage.

3. Operation of Pressure-Sensitive Gage

a. Calibration

Perform the following steps in the given order for pressure-

gage calibration:

a)
b)

c)
d)

e)
f)

h)
i)
j)
k)

Connect the strip-chart signal cable to the amplifier-
power-supply unit.

Set the tide-capacitor switch to the "capacitor-out"
position (switch contacts closed).

Apply power to the recorder and the amplifier-power unit.

Adjust the d.c. voltage out of each 60-volt power supply
to exactly 60 volts.

Adjust the d.c. voltage out of the 6-volt power supply
to exactly 6 volts.

Remove power from amplifier-power unit and strip-chart
recorder.

Connect wave sensing-unit cable to the four binding posts
on amplifier-power-supply unit. Be sure that the color
code on the binding post has been carried to the same
color code on the Sanborn linear-differential transformer
inside the pressure-sensing unit.

Set dial on the 10-turn variable resistor on the amplifier-
power unit to its counterclockwise (lowest resistance)
position.

Apply power to amplifier-power unit and strip-chart
recorder.

Adjust pen on the strip-chart recorder to center of
recording chart with lever on side of penmotor.

Decide the maximum wave height to be recorded and divide
by two.

Lower gage 1 foot into still water and readjust recorder
pen to center of chart paper with lever on side of pen-

motor.

Lower gage into water one-half of the wave height expected
to be recorded. Value found in step k above.

n) Adjust 10-turn variable resistor clockwise until recorder
pen moves to full scale.

0) Repeat steps j, 1, m, and n above.
p) Place tide-capacitor switch to "in" position (switch open).

q) Tide capacitor will begin to charge, and recorder pen
will slowly return to center of paper. When capacitor
has charged as indicated by recorder pen returning to
the center of the chart, quickly submerge the gage for
the remaining one-half value of maximum wave height ex-
pected. Recorder pen should again move to full scale on
recorder chart. Quickly move gage to a depth of 1 foot.
Recorder pen should move to opposite side of chart paper.

r) To check gage linearity, place tide capacitor switch to
"out'"' position. Place gage in 1 foot of water. Move
recorder pen to side of chart paper with lever on side
of penmotor. Submerge gage in 1-foot steps for full
wave height. Slight adjustment of the 10-turn variable
resistor may aid in setting linearity and full scale.

s) Record the dial reading on 10-turn variable resistor
and lock dial.

t) Place gage in 1 foot of water. Re-center recorder pen
on strip chart. Place tide-capacitor switch to "in"
position.

u) Gage calibration is complete; calibration may be plotted
on graph paper for further use.

If facilities are available, calibration of the gage may be carried
out by using compressed air. Such facilities for calibration would in-
clude an airtight chamber for housing the gage. This chamber should be
large enough so that it does not mechanically hinder the gage bellows.

A precision pressure gage with a suitable source of compressed air and
air valves may be used to apply the same pressure to the air chamber as
would be developed by the water depth. Calibration procedures would then
be performed as outlined above, substituting equivalent air pressure for
water depths.

b. Installation

Consideration should be given to the type cable required
for use between the pressure-sensing unit and the recording equipment
located on shore. If the surf zone is of sand, it may be possible to use
4-conductor No. 14 AWG cable having a neoprene outer jacket. This type
of cable should be taped parallel to an ordinary 1/2" diameter steel
cable through the zone of wave action. The weight of the steel cable

should cause the cable to sink well into the sand in the surf area. Slack
should be left in the cable to permit it to sink.

If the cable must pass through a rocky (or impermeable) zurf zone,
it may be necessary to use armored cable through the area where wave
action will be directly on the cable.

Cable used under water should be pressure-tested for leaks prior to
use. Most cable suppliers will make the pressure test when requested.

The short length of cable attached to the pressure-sensing unit
should be spliced to the cable from shore using a 3-M No. 82A1 cable
splicing kit.

The wave-sensing unit should be mounted to its support using the
plastic brackets shown in Figure 35. These brackets are required to
prevent galvanic action from corroding the sensing unit. The gage cable
should be taped firmly to the gage support at the point where the cable
leaves the brass gage case. If this is not done, wave action will flex
and break the cable.

Laying the cable from the recording site to the offshore sensing
point requires planning based on the gage location on the seabed. Coiling
the cable in a figure 8 on deck of the boat, barge, or other vehicle will
allow the cable to pay out without twisting. It may be desirable to lay
the cable, and then splice the gage to the end after it is in place. The
splice requires about 30 minutes to harden before placing under water.

After the gage is in its operating location and the cable laid to the
recording site, install the amplifier-power unit, the strip-chart recorder,
chart rewind, programmer, and magnetic tape recorder (if used) and connect
them as shown on Figure 40. The color code of the leads from the Sanborn
linear differential transformer must be carried to the corresponding
binding posts on the amplifier-power unit.

After the gage system is connected as outlined above, apply power to
the amplifier-power unit, strip-chart recorder, and magnetic-tape recorder,
chart rewind, and the gage is ready for operation. The 10-turn variable
resistor dial should be set to the value obtained in the calibration pro-
cedure, and the tide-capacitor switch should be set in the ''in" position
(switch open).

When the gage is first placed in operation, the recorder pen will
probably be off scale, since the tide capacitor is not in a charged
condition. The off-scale condition of the recorder pen is normal, and
the pen will slowly return to its normal position (center of chart) as
the tide capacitor charges. The tape recorder signal meter will also be
off scale as outlined above until the tide capacitor charges.

The programmer should be adjusted to provide the desired wave-record
program. The programmer will start the record at the beginning of each

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hour for a selected number of minutes. Any hour or hours may be omitted
from the recording program by removing the knurled screws from the
programmer dial.

c. Maintenance

The recording station will require servicing at regular in-
tervals to change the strip-chart recorder-paper and fill the recorder
inkwell. Also the programmer should be checked for timing accuracy.

The wave-sensing unit should be raised and inspected at 6-month
intervals to see whether it has been fouled by sea growth, and whether

the entire gage has settled into the ocean bottom and bellows operation
restricted.

Section VI. FABRICATION OF EPOXY GAGE SECTION

To make epoxy wave staff sections, a suitable mold is required. The
mold is fabricated by using a room-temperature curing silicone rubber. In
order to conserve the silicone rubber, a close fitting aluminum container
is fabricated as shown on Figure 41. A gage section pattern is also re-
quired as shown on Figure 41, for either the relay-operated wave gage, or
the other two types. The finish on the epoxy gage section will be that
of the gage pattern; care should be taken to ensure a smooth surface.

RTV-630 is available in gallon cans; the kits contain the silicone
rubber in one container and the curing catalyst in another. The silicone
rubber is used as the mold vehicle due to its releasing properties in
removing the epoxy section when hardened. Place the gage pattern in the
trough as shown in Figure 41, fill the space between the pattern and the
trough with the RTV-630 and allow to cure as specified by the manufacturer.
Use the amount of catalyst recommended by the manufacturer. Failure to
do so will shorten the pot life and cause uneven cure of the mold. Avoid
trapping air in the RTV-630 while stirring and pouring as bubbles cause
holes in the completed mold. The trough should be filled to the brim.

If excess is above the trough and gage pattern when curing is complete,

it can be trimmed with a long sharp knife. When the mold is cured, remove
the gage pattern and thinly coat the inside of the mold with vaseline.
Recoat mold with vaseline between gage section moldings.

Assembly components for the desired gage section on a jig outside the
mold and check them electrically. After checkout insert the components
in the mold as a unit and be sure that the metal gage sensing points are
in the bottom of the mold. Align the gage cable with the mold so that it
will be in the correct position when the section is completed.

After the components have been placed in the mold, fill it with one-
half the epoxy resin required for the gage section. Allow the section
to cure 4 hours and fill the rest of the mold with epoxy resin. About 7
pounds are required for one gage section. The resin is furnished in two
parts and must be mixed in equal parts by weight just prior to using. Do
not allow moisture in the resin during pouring and curing as it will cause
the epoxy to turn white. Even a good healthy sneeze over the mold will
turn the gage section white.

When the epoxy has cured (overnight) remove the section from the mold,
clean it thoroughly and recheck it electrically. Be sure the sensing tips
are not coated with epoxy.

The epoxy sections become brittle in cold weather and care should be
exercised when handling to prevent breakage.

The epoxy sections should be stored in a slotted wood board to keep

them from warping. If a section becomes warped, it may be straightened
by heating, placing in a straight position, and allowing to cool.

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Damaged sections may be returned to the mold and repaired by adding
epoxy to the injured places.

The epoxy sections may be repaired by drilling out the defective
component, replacing the component and remolding the damaged section,
using the original gage mold and new resin.

If the gage mold is not used for several weeks, it may absorb moisture
and cause the epoxy not to cure. Such moisture in the mold will also
cause the epoxy sections to be white in color. Heating the mold for
several hours should remove this moisture.

Section VII. MAGNETIC TAPE RECORDER FOR OCEAN-WAVE GAGES

1. Theory of Operation of Magnetic Tape Recorder

No commercial tape recorders are available that could be modified
to serve as an analog ocean-wave recorder for long periods of time. CERC
found it necessary to design and build its own tape recorders. The mag-
netic tape recorder Model LW-1 is designed to record ocean waves with
periods of about 2 seconds through 100 seconds. Wave heights recorded
full-signal on the tape recorder will be those from the wave gage that
provide full-scale indication on the wave gage strip-chart recorder.

The recording signal is a d.c. analog to the recording head. Line
frequency is used as the recording bias to the tape head. Thus, the re-
cording is similar to that used on a standard tape recorder for voice or
music, although a higher frequency bias is used in a standard tape re-
corder. However, at the wave period (frequency) at which the wave
recorder operates, the line frequency (60 cycles) is more than adequate.

The recording signal (wave-gage signal) from the three types of
step-resistance wave gages is a 0 to 30-volt d.c. analog. This signal is
equal to zero submergence and full submergence, respectively, of the wave
staff, thus the signal is proportional to the water level on the wave
staff. The tape recorder has a 10,000 microfarad capacitor to remove the
average d.c. signal from the wave-staff signal to prevent this average
Signal from reaching the recording tape head. This, in effect, removes
the change in gage signal caused by tidal changes. Removal of this tide
signal from the gage signal allows a wider dynamic range of the wave signal
to be applied to the tape head, resulting in a better wave recording on
the magnetic tape.

The wave-gage signal from the pressure-sensitive wave gage has the
tide component removed from the gage signal in the amplifier-power supply
unit by a high-value capacitor in much the same manner as is done in the
tape recorder. The output (wave-gage signal) from the amplifier-power
unit is a d.c. analog of 15 0 +15 volts. This signal is proportional to
the trough-to-crest wave height for the respective maximum wave height for
which the pressure-sensitive unit is calibrated. This signal will produce
full-scale movement of the recorder pen on the strip-chart recorder, and
is used as the wave signal to the tape recorder. Therefore, the tide
removal capacitor in the tape recorder is not required when the recorder
is used with the pressure-sensitive gage.

To operate the tape recorder with both types of wave gages (staff and
pressure), one requiring tide removal, the other not, there is a switch in
the tape recorder for bypassing the tide capacitor. It is labeled tide
capacitor "in-out".

The magnetic tape recorder may be operated with other wave-gaging
systems provided those gages produce a d.c. analog signal proportional

to wave height. The d.c. analog should be 0-5 volts at 1 milliampere.
Lower signals will attenuate longer period waves excessively.

Bias signal amplitude, held constant by a constant voltage harmonic-
neutralized transformer, is passed through a resistance-capacitor filter
to further improve the wave form before it goes to the recording head.

The recorder is designed to use Minnesota Mining and Manufacturing
Company No. 428 magnetic tape 1/4 inch wide, on 1,250-foot reels. One
reel of tape will record continuously for about 3 weeks. The tape speed
used is one-half inch per minute. In normal recommended operation at CERC
recording wave stations, the magnetic tape recorder operates continuously.

Tape-recorder engineering design data was not available regarding the
slowest speed that could be used. The minimum tape speed, tape-head gap,
and bias frequency, needed to record 2-second waves in the field had to
be developed in the CERC laboratory.

To provide a section of tape long enough for analysis on the CERC
spectrum analyzer, a recording must be at least 20 minutes long. While
a 20-minute record may be analyzed, a 24-minute record is recommended.

The recorder has a built-in calibrating signal (sine wave) with a
period of 4 seconds. This signal, usually recorded for 30 minutes twice
each day at 10 a.m. and 10 p.m. local standard time, is used to check
recorder operation and to standardize input to the laboratory spectrum
analyzer. The amplitude of the calibrating signal is adjustable to
provide the same signal on the magnetic tape as the full-scale signal
provided by the wave gage. The calibrating signal is programmed by a
timer plugged into the recorder chassis. A switch is provided on the
front of the tape recorder to permit the user to place the calibrating
signal on the tape at his selection. This signal must also be 20 minutes
or longer.

The recorder does not have an erase head; magnetic tape used must be
free of all recordings prior to use. When ordering, specify that tape
shall be of virgin quality and free of all test recordings. Tape should
be shipped in steel cans to aid in avoiding magnetic fields while in
transit.

Numbered, small, adhesive markers must be placed on the section of
tape that is directly over the tape head when the tape is installed and
just before it is removed. Additional markers should be similarly placed
on the tape at significant times. Markers should be logged, listing the
exact time of placement and any pertinent comments. These markers and
the data logs are the only means of identifying the time of recorded
wave data; their importance cannot be overemphasized.

Two meters are incorporated in the recorder to adjust and monitor

its operation. One has a zero center pointer, and indicates the ampli-
tude of the waves at the tape recorder. A meter movement of 400-0-400

is selected for full signal wave conditions from the wave gage. The
other indicates the current in the record head from the bias signal,
and is normally adjusted to provide a reading of 0.8 volt which corre-
sponds to 8 milliamperes of bias current in the recorder tape head.

2. Fabrication of Magnetic Tape Recorder

Parts required for the CERC LW-1 tape recorder are listed in
Table X. Details of fabrication are shown in Figures 42 through 45.

The mechanical items should be assembled to the chassis and panel
assembly. Particular care is required in aligning each electric motor
shaft and the driven shaft. Use of 1/4-inch rod drilled with a 3/16-
inch hole in one end through the panel bearings should aid in getting
good alignment of the motor shafts. Use of a similar rod drilled with
a 1/8-inch hole in one end should aid in aligning the calibrating signal
drive motor (15 r.p.m.) with the synchro shaft. When the proper alignment
is reached, the flexible couplings should receive the driven shafts
without binding. Binding at this point will cause early failure of the
flexible coupling. The panel shaft bearings should be cleaned, and given
a drop of light oil during assembly.

Wiring of the recorder is shown on the schematic diagram on Figure
46. The wiring placement is not critical in obtaining proper operation.
Good wiring practice is all that is required.

The constant-voltage transformer is mounted in the left rear of the
recorder cabinet. Input and output cables must be installed on the
transformer to provide proper connection to the plugs on the rear of the
recorder chassis.

A signal cable for the tape recorder is fabricated to the desired
length using 2-conductor No. 18 AWG and two amphenol No. 80-MC2-M
connectors.

Care is required in connecting the outer terminals of the three
potentiometers on the front panel to provide increased signal conditions
when the potentiometer shafts are turned clockwise.

The tape-supply spool shaft uses a spring and washer assembly to
provide tension to the tape. The tension of this spring should be
adjusted to provide a very light pull on the unwinding tape. If too
little tension is applied to the rewinding tape, the tape will skew on
the capstan and foul the tape drive. Correct tension is just above that
required to prevent tape skew.

Ferrous parts used in the tape transport, including the recording
head, should be demagnetized after assembly. If the tape head is mag-
netized, or if the tape is placed close to a magnetized object, the tape
recording will be of poor quality or may even be erased.

Text resumes on page 93.

Zar

257

TABLE X

LIST OF COMPONENTS FOR MAGNETIC TAPE RECORDER, LW-1

Magnetic Tape Recording Head, Brush #BK-1250

Motor, Hurst SM 1/2-1/2 RPM (Clockwise rotation)

Motor, Hurst SM-15, 15 RPM, either right or left rotation
Direct Current Microammeter - 500-0-500, Simpson Model #29

A.C. Voltmeter 0-1 Volts - 1,000 ohms per volt, Simpson
Model #49

Cabinet-Bud, No. CR-1742-HG Gray Hammertone finish
Transformer, Sola, No. 23-13-060 Harmonic neutralized type
Transformer, Stancor P-6469

Transformer, Stancor P-6134

TransfOrmer, Stancor PS-8416

Potentiometer, wire wound, 5,000 ohms, Mallory MSMPK
Potentiometer, wire wound, 2,000 ohms, Mallory M2MPK
Potentiometer, wire wound, 25,000 ohms, Mallory M25MPK
Relay, Potter Brumfield, No. MR11A-DPDT-115 volt, 60 cycles
Autosyn, No. AY-201-3-B

Cord Set, Belden #17460-S

Cable, Belden #8452

Resistor, wire wound, 1 watt, IRC, +10%, 1,000 ohms
Resistor, wire wound, 1 watt, IRC, +10%, 1,200 ohms
Resistor, wire wound, 1 watt, IRC, +10%, 560 ohms

Switch, SPST, Arrow Hart §& Hegeman, No. 20994-BF

Rectifier - 1N2070.or 1N1692

Capacitor - 100 MFD-50 volts, Aerovox PRS

ea.

€a.

ea.

€a.

ea.

€a.

ea.

€a.

ea.

fall

ea.

€a.

ea.

TABLE X (continued)

24. Resistor - 1 watt, wire wound, IRC - 2,000 ohms 2 ea.
25. Capacitor - Paper 2MFD, 200 volts - Aerovox P82Z 4 ea.
26. Idler, Wheel, Walsco, No. 1488 lexeae
27. Coupling, Millen No. 39016 Zea
28. Spring-General Cement, No. H412-F ear
29. Snap Button-Hole Plug, General Cement, H308-F SmCak.
30. Chassis, Aluminum 10" x 17" x 4", Bud AC 427 eae
31. Socket, Octal, Amphenol 78RS8 leneale
32. Plug, Harvey Hubbell No. 7485 ear
33. Plug, Harvey Hubbell No. 7484 near.
34. Plug, Harvey Hubbell No. 7486 icas
35. Plug, Harvey Hubbell No. 7487 I GEN
36. Connectors, Amphenol, male plug 80-MC2M ZRe aX,
37. Connectors, Amphenol, female receptacle 80-PC2F 1 ea.
38. Capacitor, Mallory, No. HC10100, 10,000 MFD, 10VSP lbxears
39. Bearing, Bost-Bronze, oil-impregnated bronze, Boston gear Smear.
No. FB-46-6
40. Resistor 111 ohms +1%, 1 watt, Precision Resistor Company ee ale

109 U.S. Highway, Hillside, New Jersey.
41. Plug 3-prong male with shell amphenol #160-5 imeay

42. Bearing assembly TV. Contro-Roller as per Columbia Wire pica
Supply Co., 2850 Irving Park Road, Chicago, Illinois.

43. Nameplate, brass (as desired) 1 ea.

44. Grommets, Smith 2174 Zeal.

NOTE: List does not contain raw material for machining tape guides, tape
capstan, flexible coupling for synchro, nuts, bolts, hookup wire,
or terminal strips.

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The spring for tensioning the rubber idler against the tape capstan
should be designed to place a firm pressure on the tape. If the tension
is insufficient, it will allow the tape to be pulled through the capstan
roller by the take-up reel, resulting in a tape speed too fast for proper
recording.

If the tape recorder is turned off, the capstan roller must be
backed off from resting on the capstan. If the roller is allowed to
stand on the capstan with pressure, the rubber roller will indent perma-
nently and be rendered useless. Removal of pressure on the capstan is
accomplished by placing a pin through the roller bracket into a hole
drilled in the front panel.

The recorder requires a timer for placing the internal calibration
signal on the tape automatically. Figure 47 shows assembly and wiring
of this timer. The timer cable plugs into the octal socket on top of the
tape-recorder chassis. Calibration of the tape recorder requires a
calibration unit which is fabricated according to Figure 48. Parts
required are listed in Table XI.

3. Calibration and Operation

The wave signal from the gage must have an amplitude that will
provide a current of 0.8 milliampere through the magnetic tape head.
The voltage level from the wave gage should be greater than 5 volts for
the tide capacitor in the tape recorder to have an adequate time constant.
The wave signal from the CERC wave gages is more than that required, and
the signal level is reduced and adjusted by the potentiometer in the lower
center adjusting-port in the front panel of the tape recorder. See
Figure 49.

The bias frequency to the tape head must be 8.0 milliamperes, and
is adjusted by the potentiometer located through the port on the bottom
right from center panel position.

The internal 4-second period calibration signal also must provide
0.8 milliampere through the magnetic tape head. This signal will be
indicated by the left meter on the tape recorder panel. The meter will
swing 400-0-400 microamperes when properly adjusted. A centering control
on the inside chassis of the recorder is provided to center the calibra-
tion signal on this meter.

Calibrate the tape recorder by the following steps:

a) Turn all controls recessed in the three ports in the bottom
center of the recorder panel to their counterclockwise
positions.

b) Set the centering control on the recorder chassis to its mid-
point of rotation.

Text resumes on page 98

TORK TIMER
Model No. 4100 Hourmaster

Clock Motor Winding

Switch Contacts

4 Conductor No. 18 AWG
Belden 8454 - 8 feet long.
(or length as desired )

Pin Numbers 2

Amphenol male plug 8 pin octal
No. 86CP8 with cap amphenol No. 3-24

Figure 47. Calibration signal timer for magnetic tape recorder.

NOTE: Parts mounted on Bud
Chassis No. AC- 431

DPDT
Switch

Amphenol
No. 80-PC2F

1500 Ohms
Variable Resistor

ae Volts D.C. output
Mallory M1.5 MPK

ACOPIAN CONSTANT
VOLTAGE POWER SUPPLY

Model I18A05

On and Off Switch Ss
To 115 Volts

60 Cycles

Figure 48. Diagram of Calibration Unit.

TABLE XI

PARTS REQUIRED FOR A CALIBRATION UNIT FOR CALIBRATION OF A TAPE

RECORDER WITH A STRIP-CHART RECORDER

Power Supply Output, 18 volts d.c. at 50 milliamperes
input 115 volts, 60 cycle, Acopian Technical Company,
927 Spruce Street, Easton, Pennsylvania, Model H 18A05,
or equal.

Potentiometer 1,500 Ohms, 4 watt, Mallory M1.5MPK, or equal.
Switch DPDT, Arrow Hart & Hegeman #20905 FR, or equal
Female receptacle, Amphenol #80-PC2F, or equal

Chassis aluminun, 4" x 6" x 3" Bud AC-430, or equal

Line cord, Belden, 17408S, or equal

Knob Nation Co. HR, or equal

Switch SPST, A-H §& H #20994LH, or equal

Rubber grommet for line cord

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c) Apply power to the recorder, and set the ''calibrate-signal"
switch on the front panel to the ''calibrate" position.

d) Adjust the right adjusting potentiometer on the front panel
to provide a reading of 0.8 volts on the right panel meter.

e) Adjust the left potentiometer on the front panel to provide a
swing of 400-0-400 on the left meter. If the meter does not
swing equally on each side of zero, adjust the centering
control on the recorder chassis to obtain equal movement of
the meter pointer on each side of center. Due to the inertia
of the meter movement, the meter pointer will not provide an
accurate indication of the actual current in the meter. To
get the precise peak pointer-movement of the meter, it is
necessary to stop the synchro shaft at its peak signal point
of rotation. To do this, set the switch on the chassis near
the synchro to the "calibrate'' position, and grasp the coupling
attached to the synchro shaft and turn it manually to provide
peak indication on the left panel meter. Adjust the panel
control for the proper 400-0-400 movement of the meter corre-
sponding to the physical location of the synchro shaft that
produces maximum swing of the meter. The centering control
may require further adjustment at this time. Adjustment of
the caltbration stgnal ts very important as it ts used to
standardize the wave gage signal and the spectrum analyzer
tn the CERC laboratory. Return the calibrate switch near the
synchro to its "operate'' position when the above adjustment
is completed.

f) Connect the signal cable from the magnetic tape recorder and
the signal cable from the strip-chart recorder to the calibra-
tion unit as shown on Figure 50.

g) Set the voltage-control potentiometer on the top of the cali-
bration unit to its counterclockwise position.

h) Apply power to the tape recorder and strip-chart recorder, and
set the calibrate switch on the front panel to "off".

i) Adjust the strip-chart recorder pen to the center line on the
recording chart using the manual control on the penmotor.

j) Place the tide-capacitor switch on the tape recorder chassis to
the "out" position (switch closed).

k) Apply power to the calibrate unit, and adjust the strip-chart
recorder pen for full-scale indication (one-half of chart width)

using the voltage-control potentiometer on the calibration unit.

1) Adjust the bottom center control on the tape recorder panel to

To 115 Volt 60 Cycle

Power Line To 115 Volt 60 Cycle
Power Line

MAGNETIC TAPE
RECORDER

STRIP CHART
RECORDER

Recorder Pen Motor
Signal Cable

Magnetic Tape Recorder
Signal Cable

To II5 Volt 60 Cycle
Power Line

CALIBRATION UNIT

Figure 50. Block Diagram of Calibration hookup.

provide an indication of 400 microamperes on the left mag-
netic tape recorder meter.

m) Move the polarity-reversing switch on the calibrate unit
to its other position. The strip-chart recorder pen should
indicate full scale on the other side of the chart paper,
and the magnetic tape recorder signal meter should indicate
400 microamperes on the opposite side of zero from that
found in 1) above.

n) Readjust the bias meter signal to 0.8 volt. When switching
from "'operate'' to "calibrate", the bias meter will change
slightly; this is normal, and will not affect recorder
operation.

o) The magnetic tape recorder is now calibrated for full-scale
recording of the signal that produces full-scale movement
of the strip-chart recorder pen. Since the strip-chart
recorder pen indicates the maximum wave height produced
by the wave gage, the magnetic tape recorder is also so
calibrated.

Since all strip-chart recorders do not have the same sensitivity,
the wave-gage circuitry is adjusted to overcome this deficiency when the
wave gage is calibrated. Therefore, the calibration of the magnetic tape
recorder must be mated with the calibration of the strip-chart recorder
with which it operates.

100

Section VIII. MODIFICATION OF STRIP-CHART RECORDER SPEED

The slowest speed of the chart on the recorder as received from the
manufacturer is 5 millimeters per second or about 12 inches per minute.
To conserve chart paper and lengthen the time between visits to the wave
recording station, it is desirable to change the chart speed to a lower
value.

Three lower chart speeds can be provided for the recorder with
fairly simple changes in the gears. These changes will provide a basic
chart speed of 2.5 millimeters per second, 1.25 millimeters per second,
or 1.0 millimeter per second.

Recorder paper comes in rolls 300 feet long on GSA schedule from
Judson Bigelow, Inc., 12-12 44th Avenue, Long Island City, New York,
Chart No. RA-2911-30 JB. With the recorder operating for 7 minutes each
4 hours and the reduced chart speed of 2.5 millimeters per second, a
300-foot roll will last about 14 days. If different frequency recording
periods are desired, the time span for one roll may be calculated.

If the recorder is modified to a slower chart speed, wave crests
will appear closer together on the chart. A sample of wave periods,
using Sine waves, on a recorder chart with speeds of 2.5 millimeters,
1.25 millimeters, and 1.0 millimeter per second are shown on Figures
51, 52, and 53.

To modify the recorder chart speed, proceed as follows:

a) Fabricate the required gear assemblies and parts for the
selected chart speed as shown on Figures 54 through 56.

b) Remove the recorder pen.
c) Remove the chart platen.
d) Remove the chart payout guide and paper tear-off unit.

e) Remove the chart driving roller, taking care not to lose the
two brass spacers on the ends of the roller.

f) Remove the chart speed-shift knob assembly. A thin knife blade
“in the side of the main drive-shaft slot will accomplish this.

g) Remove the snap spring on the main drive shaft. Observe the
spacing between the spring and the recorder frame, and retain
this distance when recorder is re-assembled.

101

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Figure 51. Wave records with chart speed of 2.5 millimeters per second

102

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Figure 52. Wave records with chart speed of 1.25 millimeter per second.

103

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Figure 53. Wave records with chart speed of 1.0 millimeter per second.

104

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107

h) Remove nuts from secondary gear-cluster shaft.

i) Loosen set screw in collar on left side of recorder main
drive shaft.

j) Remove the side frame of the recorder from the recorder base
opposite from the motor.

k) Remove large gear from left side of main gear shaft.

1) Remove spacer which holds the smallest gear on main
drive shaft.

m) Place new gears and spacers on main drive shaft and on
secondary gear-cluster shaft as shown on Figures 57 and 58.

n) Re-assemble recorder, and tighten setscrews in spacers: and
new drive gear.

o) If gear assembly binds when re-assembled, some hand-fitting
of the spacers may be required.

The gear train should run freely when it is properly adjusted.
Lubricate the shafts and gear trains when reassembling. The re-

corder gear assembly before and after modification is shown on Figures
57 and 58.

108

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Section IX. ANALYSIS OF OCEAN WAVE GAGE RECORDS

Step-Resistance Wave Gages

Strip-chart recordings taken at CERC ocean wave recording sta-

tions are analyzed for significant wave height, Hs, and significant wave
period, Ts.

The visual method used in analyzing strip-chart recordings (as opposed
to automatic magnetic tape analysis) for a significant wave height and wave
period follows:

From a chart run (normally 7 minutes), select as nearly as
possible the minute with a wave train which contains most of
the highest and most uniform waves.

Determine the period of the wave selected in step a) by using
the wave-period template according to instructions (Figure 59).
When the wave period on the chart falls between two of the
periods shown on the template, the analyst may approximate
what he considers will be nearest to the exact period. For
example, if the period is about halfway between the 5-second
template and the 6-second template, then the period is about
5.5 seconds.

Use the listing below to determine which wave should be
measured to get the approximate significant height of the
waves. The wave-height template will aid in determining
which wave is to be measured for height.

Wave period (seconds) Wave to measure
3 3rd highest
SES 3rd highest
4 2nd highest
5 2nd highest
6 2nd highest
7 2nd highest
8 or longer Ist highest

With the proper wave-height template (Figures 60 and 61),
determine the height of the wave given by step c) by finding
the rectangle on the template whose top line comes nearest to
to the crest when the bottom line is on the preceding trough.
The wave height, in feet, is indicated by the number on the
rectangle.

Records with wave heights less than 1/2-foot are listed on the
compilation sheet (Figure 62) as calm - without listing the
wave height. However, the significant wave period for such
records is determined and is indicated on the compilation
sheet.

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Figure 60. Sample of wave-height template (Fabricate from clear acetate
using proper gage calibration.)

113

Figure 61. Sample of wave-height template (Fabricate from clear acetate
using proper gage calibration.)

114

Location Gauge Recorder

ATLANTIC CITY N J STAFF BRUSH
TIME TIME
DATE OF PERIOD HEIGHT DATE OF PERIOD HEIGHT
1965 START (SECONDS ) ( FEET ) (SECONDS ) (FEET )
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BEB-100

Figure 62. Wave-data compilation sheet.

2. Pressure-Sensitive Gages

Due to the depth-period attenuation present when wave record-
ings are taken using a pressure sensor placed near the ocean bottom,
the recordings will require a correction factor to obtain a true wave-
height reading.

To obtain the true wave-height data (significant height and sig-
nificant period), use the following procedure:

a) Determine the significant height and period outlined in the
in the method for step-resistance gages.

b) Using the significant period refer to Figure 63 and find the
line representing this wave period.

c) Determine the water depth at the time the recording was taken.
d) Intersect the water depth and wave period on the period curve.
e) Read the K (response) factor below the point of intersection.

f) Divide the significant height (found in a) above) by the
K factor to obtain a corrected wave height.

The curves apply only to a wave gage mounted on the ocean bottom.
If the gage is mounted near the surface, additional curves will be
required. Data for preparing these curves (K factor) is available on
page D2 and Tables D-1 and D-2 of CERC Technical Report No. 4, "Shore
Protection. Planning and Design", 3rd Edition, 1966.

116

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UNCLASS IF [ED

Security Classification

DOCUMENT CONTROL DATA-R&D
(Security classification of title, body of abstract and indexing annotation must be entered when the overall report is classilied

1. ORIGINATING ACTIVITY (Corporate author) 2a. REPORT SECURITY CLASSIFICATION
Coastal Engineering Research Center (CERC) UNCLASS IFIED

Corps of Engineers, Department of the Army
Washington, D. C. 20016

3. REPORT TITLE

CERC WAVE GAGES

4. DESCRIPTIVE NOTES (Type of report and inclusive dates)

5- AUTHOR(S) (Firat name, middle initial, last name)

Leo C. Williams

6. REPORT DATE 7a. TOTAL NO. CF PAGES 7b. NO. OF REFS
December 1969 124 0

8a. CONTRACT OR GRANT NO.

9a. CRIGINATOR'S REPORT NUMBER(S)

b. PROJECT NO.

Technical Report No. 30

9b. OTHER REPORT NO(S) (Any other numbers thet msy be aesigned
this report)

10. DISTRIBUTION STATEMENT
This document has been approved for public release and sale; its distribution
is unlimited.

11. SUPPLEMENTARY NOTES 12. SPONSORING MILITARY ACTIVITY

CERC has used wave gages to gather prototype wave data since 1948. Two
basic types of gages are now used in the field - the step-resistance staff
gage and the underwater pressure-sensitive gage. CERC has developed three
types of step-resistance staff gages - a series type for use in fresh water,
a parallel type for use in salt water, and a relay-operated type for use in
either fresh or salt water or in water where wide changes in salinity occur.
The pressure gage can be used in water of any salinity. The series and
parallel gages have an accuracy of +5 percent plus the spacing of one sensor
increment. The relay gage has an accuracy of +2 percent plus the spacing of
one sensor increment. The accuracy of the pressure-sensitive gage is not as
precise as that of the step-resistance gages. The report describes each gage
and the theory of operation, details of fabrication, steps for calibration
and installation, and requirements of maintenance.

DD 2%"..1473 Secoctre Pon smu usc. en? UNCLASSIFIED

curity Classification

UNCLASSIFIED

Security Classification

KEY WORDS

Ocean-wave gages

Oceanographic instrumentation
Step-resistance wave gages
Strip-chart wave records

Magnetic tape wave records
Wave-record analyzer (magnetic tape)

UNCLASSIFIED
Security Classification

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